Escher jokes aside, some people do experience this phenomenon and have no idea why. It’s actually really simple.
When you sign your name, stir soup, open a door or scratch your nose, the reason you can do these things quickly and accurately without thinking about it is muscle memory.
Muscle memory is our most powerful tool. It is what happens when you repeat an action to the point where the brain no longer has to get involved – the impulses in the nerves happen automatically. It’s how you learn to walk, drive a car, or how sportspeople get to the top of their game through training. Your body learns a default set of actions, and learns what to expect in return.
So think about how you learn to navigate stairs. As a child, you probably had child locks and baby doors to stop you falling anywhere. But there is one place where you repetitively climb steps over and over and train your muscle memory from a very young age. The playground!
Your developing brain learns how to climb stairs by climbing slides, and your body learns to expect a drop-swoosh-WHEEEE!-clunk at the end. This routine is sometimes programmed in so well that we don’t grow out of it as an adult and the expectation of falling remains.