You know what it's like, when you've been thinking hard about something, working it round and round in your head. It feels like it's hollowed you out, as if you're a chess grandmaster who's burned 6,000 calories sitting in a chair. Look at the words we use to describe how we feel at these times: drained, burned out, running on empty, nothing left in the tank, strung out.

We talk as if our brain is a battery, and too much thinking drains it.

In reality, your brain is about 2% of your bodyweight (yes, even you!), but uses around 20% of your energy at rest. On average, that's four hundred calories a day, just to idle along. Surprisingly, despite how it feels, studies have shown that hard thinking doesn't require much more energy than if we're not actively thinking at all. Most of our brain activity is used up by that vast, unconscious background activity that keeps everything going so you can think about thinking, and that's the same whether you're wrestling a difficult quadratic equation, vegging in front of Love Island or staring out of a train window. So why does thinking feel so expensive?

When you concentrate hard for a long stretch, focusing attention, holding off distractions,, a chemical by-product accumulates in the executive part of your brain, almost like lactate building in muscles at the end of a long run. The interesting thing is, your brain adapts to being worked in a similar way to a muscle. When people learn to juggle, the part of their brain that tracks movement physically thickens within weeks. Spend years learning a city's streets, as London cab drivers do, and the region that holds spatial awareness grows to match. In this way, effort builds brainpower. But the plasticity of our neurobiology means if you stop making the effort, your brain quickly loses the ability to do the thing. Use it, or lose it.

We've started to see this phenomenon in action when skilled people lean on AI for difficult tasks. When hospitals brought in an AI tool that highlighted pre-cancerous growths during colonoscopies, doctors got better at spotting them with the tool switched on, but their unaided detection had dropped by around a fifth after just three months.

So here's a question for you to think about on your summer break: what are you still doing the hard way, on purpose, to ensure you stay good at it? I believe we're been thinking about 'efficiency' all wrong. I think the value of effort is both what it builds in you (a trained eye, expert judgement), and something less tangible - what it deposits in the thing you create.

Lewis Hyde argued that a work of art is not a commodity: 'Where there is no gift there is no art.' A friend once told me how her mum had rejected a birthday card she'd made as a child because she hadn't taken enough time over it. Her mother didn't doubt the love; she doubted the effort that would have made it worthy.

A machine can assemble something flawlessly, but all too often it leaves a space where the human should be. And you feel that absence the way my friend's mum did - it holds no weight. There's a word from critical theory, cathexis, for the emotional energy we invest in a person or thing, but I couldn't find a word for this emotional charge held inside the 'gift' from the creator. So I made one up!

empathexis (em-path-EX-is) n. - the emotional energy, spirit and intention of a maker, held within the thing they have made; lived experience embodied in a work, distinguishing it from what's produced by technique, imitation or process alone.

None of this is a case for doing things the hard way for its own sake; a thing can be effortful and still empty. The point is what the effort is for. Instead of handing it off to AI, why not keep some of the hard thinking for yourself, not in spite of the effort, but because of it. The struggle, it turns out, isn't the strife - it's the gift.