Yesterday I wandered into Waterstones and picked up Arnold Schwarzenegger’s new book, Be Useful: Seven Tools for Life, on the day it came out.

I like books anyway, particularly proper physical ones that end up battered, folded over and sitting on a shelf as a reminder of what you were interested in at a particular point in your life. This one caught me because of the title as much as anything. Be Useful is such a simple instruction, and it happens to align pretty closely with something I’ve always believed about time: whatever hours you have available, try to do something useful with them.

Then I remembered an unfinished article about sleep sitting somewhere in my old notes.

I found it, checked the date and laughed. I had started writing it on 10 October 2016. Arnold’s book came out on 10 October 2023, exactly seven years later.

Apparently the best way to demonstrate a belief in using time wisely is to leave an article about it unfinished for seven years.

The old version is quite funny to read now. There are bits I still agree with, chunks of research pasted in from different places, several Steve Jobs quotes because apparently that was compulsory in 2016, and a slightly obsessive attempt to work out whether sleeping less meant somehow getting more life.

The question itself still interests me, though.

How much sleep do we really need, and what exactly are we doing with the hours when we’re awake?

Eight hours has always bothered me

Sleep is one of those things most of us think we understand because we’ve been told about it since childhood. Go to bed at a sensible time, get eight hours, don’t stay up all night and everything will be fine.

Ask somebody how much sleep they need and they’ll generally give you a surprisingly precise answer. Eight hours. Nine hours. Six and a half. Some people will tell you they simply cannot function without a particular amount, while somebody else will proudly explain that they have survived on four hours a night since 1998.

I used to say I needed eight or nine because that was what I assumed a proper night’s sleep looked like.

The arithmetic was the part that always bothered me. There are 24 hours in a day, so eight hours asleep means spending a third of it unconscious. Apply that across an entire lifetime and the number becomes slightly uncomfortable. We’re talking about decades of our lives spent asleep.

My instinct has always been to look at that and wonder whether some of those hours could be put to better use.

That probably says as much about me as it does about sleep.

I don’t particularly like wasting time. I don’t mean that in the modern productivity sense where every spare fifteen minutes should apparently become a side hustle, a podcast or an opportunity to improve your personal brand. I quite enjoy doing nothing when I have deliberately decided to do nothing.

What frustrates me is time that disappears without achieving anything or being particularly enjoyable.

A meeting that could have been an email. Filling in the same information for the third time because two systems don’t speak to each other. Watching something I’m not actually interested in because it’s easier than switching it off. Picking up my phone to answer one message and eventually realising I’ve spent half an hour looking at things I couldn’t tell you about five minutes later.

That kind of time feels expensive to me because there is no way of getting it back.

Arnold and the six-hour thing

Arnold has been making the same joke about sleep for years. There are 24 hours in a day, he sleeps for six and that leaves eighteen. If you say you need eight hours, his answer is basically that you should sleep faster.

It’s a very Arnold Schwarzenegger way of making a point.

I don’t take it as medical advice, and nor should anyone else. Current sleep guidance is fairly clear that most healthy adults should regularly be getting at least seven hours, and there are very good reasons not to turn chronic sleep deprivation into some strange badge of ambition.

But I understand what he’s getting at.

The useful part of the idea isn’t really the six hours. It’s the eighteen.

What are you doing with them?

I’ve always thought of it as being useful in the hours. That doesn’t necessarily mean working. An hour spent with your children is useful. An hour talking to a friend is useful. Reading something interesting, learning how something works, playing sport, building something entirely unnecessary because you’re curious, going somewhere new, fixing the stupid thing in the house that has annoyed you for six months, all of those count.

Even sitting quietly doing absolutely nothing can be useful if that’s genuinely what you need.

The difference, for me at least, is intention. I dislike looking back at an evening or a day and realising the time simply vanished.

Sleep makes that idea awkward because reducing it appears, on paper, to create more hours.

If you sleep six instead of eight, you’ve gained two hours a day. That’s fourteen hours a week and more than seven hundred hours over a year. Look at the number like that and it sounds enormous.

Except the maths is missing something fairly important.

The quality of the hours.

Being awake isn’t the same as being useful

This was the biggest problem with the original version I wrote in 2016. I had found some interesting research around sleep deprivation and performance, particularly the fact that somebody who is tired can sometimes perform perfectly well when concentrating hard on a specific task.

I found that fascinating because it appeared to support something I’d seen plenty of times in real life. Somebody can have hardly slept and still look completely alert in a meeting, solve a problem, write code or produce something good.

The failure tends not to happen while you’re forcing yourself to concentrate. It happens when concentration drops, as it naturally does throughout a day. A properly rested brain is better able to recover its attention. A tired one becomes inconsistent.

That makes sleep deprivation deceptive.

You can still function. You can still talk, work, answer emails and convince everybody, including yourself, that you’re fine. What becomes harder to see is the gradual loss of judgement, patience, memory and concentration.

I’ve certainly experienced that.

There are nights when working late has been brilliant. The house is quiet, messages have stopped arriving and I’ve been completely absorbed in solving something. Some of my best thinking has happened during those hours because there was finally nothing else competing for attention.

There have also been nights when I’ve stared at the same problem for two hours, becoming increasingly determined that I was going to solve it before going to bed, only to wake up and fix it almost immediately the next morning.

That is a fairly humbling demonstration of what sleep can do.

If I gain two waking hours by sleeping less but then spend three hours the following day being slower, less creative and slightly grumpier, I haven’t discovered additional time. I’ve just redistributed it badly.

Sleep is probably maintenance rather than lost time

That’s where my thinking has changed most since I first wrote this.

In 2016 I was looking at sleep mainly as time consumed. If I slept eight hours, those were eight hours unavailable for everything else.

I don’t think that is the right way to think about it anymore.

Sleep is closer to maintenance.

There’s a temptation, especially if you enjoy building things or running businesses, to regard maintenance as something that interrupts productive work. Anyone who has managed software or machinery knows where that eventually leads. You can postpone maintenance and enjoy a little more output for a while, but the underlying system doesn’t stop accumulating the consequences.

Human beings appear to be annoyingly similar.

Sleep is involved in memory, attention, physical recovery, immune function and a collection of other things I am not qualified to explain in any useful scientific detail. What matters to me is simpler: I am obviously better at most things when I’ve slept properly.

That makes the trade rather different.

If eight hours of sleep gives somebody sixteen genuinely good waking hours, that may be a far better use of a day than six hours of sleep followed by eighteen mediocre ones.

Equally, I don’t think eight should become a target people worship regardless of how they actually feel. Sleep needs vary, and duration is only part of the equation. Seven solid hours at roughly consistent times can be very different from eight hours spent repeatedly waking up or staring at the ceiling.

The better question is probably whether the sleep you’re getting leaves you properly functional for the life you’re trying to live.

Modern life isn’t exactly helping

The other thing that has changed dramatically since I started the original article is the amount of our lives now fighting for attention.

Phones were obviously already part of life in 2016, but the relationship has only become more intense. We carry work, news, entertainment, friends, arguments, games, shopping and effectively the collected knowledge of civilisation in something that sits on the bedside table.

Then we wonder why our brains don’t politely shut down the moment we turn the light off.

There is something slightly absurd about spending the evening worrying that we aren’t getting enough sleep while holding a device deliberately designed to make putting it down difficult.

Stress has a similar feedback loop. You sleep badly because something is on your mind, then deal with it less effectively the next day because you’re tired, which gives you more to think about when you go back to bed.

None of this has a particularly exciting solution. Regular sleeping hours help. Less bright screen light immediately before bed helps. A quiet, dark room helps. Exercise helps many people. If you genuinely have persistent sleep problems, proper medical advice is probably more useful than another productivity blog telling you to wake at 5am.

Annoyingly, quite a lot of sensible health advice is boring.

Be useful in the hours

So I still like Arnold’s six-hour story, even though I don’t intend to organise my sleep around it.

The line reminds me that time is finite, and that’s enough.

Be Useful isn’t really a complicated instruction. The interesting part is deciding what useful means to you.

I don’t want every hour optimised. I don’t want a Sunday afternoon to require measurable output, and I certainly don’t want every hobby eventually converted into another business.

I do want to be present in the things I’ve decided are worth my time.

If I’m working, I’d rather work properly than spend twice as long pretending to. If I’m with people I care about, I’d rather actually be there. If I’m learning something, I want to pay attention. If I need to rest, I would rather admit that and rest properly than spend two hours half-working and half-doing nothing.

And if sleep is what makes the rest of those hours better, then perhaps it isn’t taking as much from us as the arithmetic suggests.

I’m still not completely convinced I need eight hours every night. Arnold apparently manages on six. Somewhere between those numbers is probably whatever works best for me at that particular point in life.

What I am much more convinced about, seven years after starting this, is that simply being awake for longer isn’t the same as having more time.

The useful hours are the ones that matter.

I’m going to try not to waste too many of them.

Although based on the turnaround time of this article, I probably shouldn’t make any promises.

And the original?

When I went looking for this article, I found the version I actually started writing on 10 October 2016.

I was tempted to quietly borrow the useful bits and pretend the rest had never happened, but that feels like cheating. It is quite a good snapshot of what I was reading, thinking about and apparently quoting far too much at the time.

So I’ve left it as it was. You can read that original 2016 version here:

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The beauty of sleep

10 October 2016

A good night’s sleep is the secret to success. Or is it?

Everyone needs a good night’s sleep.

We’re constantly told that sleep is the key to functioning properly during the day, maintaining good health and generally being a more useful human being. At the same time, an enormous number of people struggle to sleep well, whether because of stress, insomnia or simply because there never seem to be enough hours in the day.

I’ve become increasingly fascinated by sleep because, when you actually stop and think about it, we spend an extraordinary amount of our lives doing it.

If you average eight hours a night, that’s a third of every day. Across a lifetime, potentially something like 24 years asleep.

That’s a pretty long time.

And it makes me wonder how much we really understand about something we spend so much time doing.

Most of what I’ve always believed about sleep probably came from the same places as everybody else: parents, teachers, television, things I’ve read and things people confidently repeat because somebody once told them the same thing.

Eight hours is good.

Going to bed early is good.

Being tired is bad.

Simple enough.

Except the more I’ve read about sleep, the less simple it appears to be.

Catching up on ZZZs

For some people, lack of sleep isn’t really insomnia. It’s lack of time.

Work runs late. Children wake up. Something needs finishing. You stay up watching something. You tell yourself you’ll catch up at the weekend.

One of the things I found interesting while looking into this was the idea of recovery sleep. Missing an hour doesn’t necessarily mean you need to repay exactly one hour later. The body appears to be more flexible than that, and a few decent nights can make a substantial difference after a period of poor sleep.

That doesn’t mean chronic sleep deprivation is harmless, though.

One of the recurring themes in the research is that people aren’t always particularly good at judging how badly tiredness is affecting them.

Someone can tell you they function perfectly well on very little sleep and genuinely believe it.

That doesn’t necessarily make it true.

A tired person can still concentrate intensely on something and perform well. The interesting difference appears when concentration naturally drops. A rested brain can recover attention much more effectively. A sleep-deprived one struggles.

That makes tiredness quite deceptive.

You can still work.

You can still think.

You can still get things done.

You’re just less consistent at it.

Which raises an interesting question about all those late nights spent trying to get ahead.

Is an extra hour of work actually useful if your brain is performing worse while you’re doing it?

The eight-hour sleep myth

Everyone I’ve asked seems to have an answer to the question, “How much sleep do you need?”

A common one, and one I’ve given plenty of times myself, is something like:

“I need my eight or nine hours. I know that.”

But why?

Why eight?

The interesting thing is that there doesn’t appear to be one perfect number that applies equally to everybody.

One piece of research I came across from sleep researcher Daniel Kripke suggested that people reporting around 6.5 to 7.5 hours of sleep had some of the best outcomes in the population he studied.

That doesn’t suddenly mean everybody should aim for six and a half hours, any more than being told eight hours is healthy means every person must sleep for exactly eight.

The more useful point is that sleep isn’t as simple as reaching an arbitrary target.

Quality matters.

Consistency matters.

And individuals are different.

That’s what I find fascinating.

You can meet somebody who has slept for four or five hours and appears every bit as alert as somebody who had eight. For a while, perhaps they genuinely are.

The problem seems to arrive when attention drops.

Both rested and sleep-deprived people lose focus. That’s normal. But a rested brain is much better at compensating and bringing attention back.

A tired one isn’t.

So perhaps the danger isn’t that being tired makes you immediately incapable of doing anything.

It’s that your ability to recover starts failing without you necessarily noticing.

Sleep, stress and switching off

Stress seems to be closely connected to sleep too, which isn’t especially surprising.

The more stressed you are, the harder it can be to switch off. Then poor sleep makes dealing with stress harder the following day, creating a fairly unpleasant loop.

There are plenty of theories about why this happens.

Stress can create a state of vigilance that doesn’t sit particularly comfortably with sleep. Sleep requires us to stop paying attention to the environment around us and effectively let go for a while.

If your brain believes there is still something to worry about, that’s difficult.

Anyone who has gone to bed exhausted only to discover that their brain has chosen that exact moment to start solving every problem in their life will recognise it.

Some of the simplest advice appears to be the most useful.

Keep reasonably regular sleeping and waking times.

Keep bedrooms quiet and dark.

Avoid filling the final hour of the day with bright screens if possible.

Give the brain some indication that the day is actually ending.

None of this is especially revolutionary, but perhaps that’s the point.

Meditation, mindfulness and sleep

Another area I’ve been reading about is mindfulness and meditation.

A 2015 study involving older adults found that a short mindfulness programme improved sleep-related measures compared with a group receiving sleep education alone, while also reducing fatigue and depression symptoms.

Six sessions.

That’s interesting because meditation isn’t really doing anything to sleep itself.

It’s changing what happens immediately before sleep.

Quietening the mind.

Reducing stress.

Stopping some of that relentless internal conversation that seems determined to start just as the lights go out.

I suspect there’s something useful in that beyond formal meditation too.

Most of us spend the day continuously consuming information and then expect our brain to instantly shut down because we’ve decided it’s bedtime.

Perhaps some sort of transition isn’t a bad idea.

Sleep and learning

Sleep seems especially important for learning and memory.

One idea I particularly like is getting students to keep sleep diaries: record when they went to bed, when they woke up, roughly how long they slept and how alert they feel the following day.

Not because children need another spreadsheet in their lives, but because seeing the relationship for themselves is probably more persuasive than simply being told to go to bed earlier.

If somebody notices they concentrate better, remember more or perform better at sport after sleeping properly, sleep becomes something practical rather than another instruction from an adult.

There is also research suggesting short naps can improve alertness and concentration.

Again, not necessarily because everybody needs to start sleeping all afternoon, but because sleep clearly isn’t just dead time.

Something useful is happening.

We know surprisingly little

Perhaps that’s what I find most interesting.

Sleep is so ordinary that we assume we understand it.

Everyone does it.

Everyone has an opinion on it.

Everyone knows what it feels like to have too little.

Yet a surprising amount of what we currently know about sleep has only been established relatively recently, and there are still enormous gaps in our understanding.

Why exactly do we need it?

Why do different people need different amounts?

Why do some people seem naturally comfortable sleeping for much less?

Why do we dream?

Why does missing sleep affect some types of performance much more dramatically than others?

Something we spend roughly a third of our lives doing still contains plenty of unanswered questions.

And what about the hours we’re awake?

This is probably the bit that started me thinking about sleep in the first place.

Steve Jobs once said:

“We don’t get a chance to do that many things, and every one should be really excellent. Because this is our life.”

That idea has always resonated with me.

Life is brief.

The number of genuinely useful hours we get isn’t unlimited.

So there’s an obvious temptation to look at sleep and wonder whether we are wasting too much of that limited time unconscious.

Could I sleep less?

Could I get another hour?

Could I achieve more?

The answer, frustratingly, seems to be that simply being awake for longer isn’t necessarily the same as having more useful time.

An extra hour is only valuable if you’re capable of doing something worthwhile with it.

Sacrificing sleep to create more working time can easily become self-defeating if concentration, creativity and judgement deteriorate as a result.

Perhaps the goal isn’t to sleep as little as possible.

Perhaps it’s to sleep efficiently enough that the hours left over are good ones.

I still don’t know exactly how much sleep I need.

I’m increasingly unconvinced that anybody has one universally correct answer.

But given how much of our lives sleep occupies, it feels like something worth understanding rather than simply accepting the number we’ve always been told.

And if I can work out how to get everything I need from slightly fewer hours?

Well, I can probably find something to do with them.

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Original draft: 10 October 2016. Left as the argument I was making at the time.