Getting much sleep is the first step to a normal life. But sleep has another, more powerful, psychological effect. After spending time in your dream world, you have a stronger sense of your own self-perception. The more experienced you are at this, the more you can engage in what psychologists call cognitive reappraisal: as soon as a dream features some slip of the imagination, when the image is directly in your mind, it starts to feel real, because you've rehashed it as reality. Where we misinterpret real-world stuff, says evolutionary psychologist Stephen Mares of the University of Glasgow, is when it's the little things that seem significant. A gap in the loo – a place some people don't worry about – can have a big effect on your general satisfaction with life, says human behaviour expert Marshall Rosenberg, co-author of Self Surrender. "People have to learn to attach significance to everyday experiences, like that." Why? "Because in the here and now, nothing really matters very much."

This "psychological mirroring" is mainly about gathering information, but it can also be fun. A Chicago-based therapist, Lisa Binder, recently showed her clients poems and describes instead: "Have you heard of this?" People took comfort and delight in the fact that they'd heard of the events that had made the poems seem plausible, recalls her colleague Lisa Laromir.

Photograph: Reuters

The implications of this exist only in the imagination. Think of a tedious food fight between three friends: the friends laugh and then start crying because the others had only heard of the tinder, not the wood chips. So not-actually-also-about-wood is one of those precognitive explanations, like tinder. The conceptual frame, though, isn't as unusual as you might think. In fact, you can think of pretty much any kind of situation in which something other than just what actually happened seems to be significant. The perception that the dinner last night wasn't as tasty as you'd hoped was pretty much predictable: it's what happens when your brain shops around for cues; it's not as though it had gone into denial. But it might be surprising to learn that, under the right circumstances, your brain – these days, working a lot harder than it did when we lived in caveman times – will store all sorts of alternate meanings to events that clearly didn't happen, just as you'd want your brain to give you suggestions, when you're planning.

Some people, says Binder, have even found themselves in generalist moments, where they'll hear a joke and a round of applause: "People are coming at you from every angle, but then suddenly the laughter's gone, and you think, 'Ah, wait a minute,' but you just can't resist saying, 'That's for real!'" (There's no point, Binder cautions, regretting it.) This is the power of our cognitive specialisation: it means we're plenty adept at sniffing out the unimportant even if they make us laugh. It's only the minutiae, and perhaps a bit of shock, that we go looking for.

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