Why is it nearly impossible to tickle yourself?

It is nearly impossible to tickle yourself because your brain, with help from a region called the cerebellum, continuously predicts the sensory consequences of your own movements and dampens the resulting sensation. Tickling depends heavily on surprise, and your brain's accurate prediction of exactly when and where your own fingers will touch your skin removes that surprise.

Explanations involving hand warmth are not accurate, temperature has nothing to do with why self-tickling fails, and the claim that you can actually tickle yourself easily runs directly against what most people experience and what this brain mechanism explains.

Researchers have even used specially designed machines that introduce a slight, unpredictable delay between a person's own hand movement and the resulting touch, and under those conditions people do begin to feel a ticklish sensation from their own touch, supporting the idea that surprise, not the touch itself, is what makes tickling work.