To understand why, you need to know more about how your brain works. One of its main tasks is to try to make good guesses about what’s going to happen next. While you’re busy getting on with your life, walking downstairs or eating your breakfast, parts of your brain are always trying to predict the future.

Remember when you first learned how to ride a bicycle? At first, it took a lot of concentration to keep the handlebars steady and push the pedals. But after a while, cycling became easy. Now you’re not aware of the movements you make to keep the bike going. From experience, your brain knows exactly what to expect so your body rides the bike automatically. Your brain is predicting all the movements you need to make.

You only have to think consciously about cycling if something changes — like if there’s a strong wind or you get a flat tyre. When something unexpected happens like this, your brain is forced to change its predictions about what will happen next. If it does its job well, you’ll adjust to the strong wind, leaning your body so you don’t fall.

Why is it so important for our brains to predict what will happen next? It helps us make fewer mistakes and can even save our lives.

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Because your brain is always predicting your own actions, and how your body will feel as a result, you cannot tickle yourself. Other people can tickle you because they can surprise you. You can’t predict what their tickling actions will be.

And this knowledge leads to an interesting truth: if you build a machine that allows you to move a feather, but the feather moves only after a delay of a second, then you can tickle your- self. The results of your own actions will now surprise you.