"Hey doc, I laugh when someone else tickles me. So why can't I tickle myself?"

That's a great question, and I'm tickled to say I've got an answer for you.

The reason you giggle when someone else tickles you is that tickling catches your brain off-guard.

Even if you see those fingers coming at you, you still laugh--it's kind of a nervous reaction.

But you can't tickle yourself because a part of your brain called the cerebellum is constantly monitoring what you're doing. If you reach for wherever your tickle spot may be, your brain knows exactly what your intentions are, and it goes on guard, blocking those ticklish impulses.

But that's ok--if we could tickle ourselves there'd be no purpose for big brothers!