Why are we unable to tickle ourselves?

It is because you need someone to surprise you, if you're expecting it it won't work.

right after i read this i looked into my girlfriend's eyes and said "im gonna tickle you now" and the moment i tickled her she went nuts. i think she was really expecting it.

Hmm to be quite honest, I can still tickle myself on my feet. I believe because your feet is basically the end of all your nerve endings down below, light touching excites the nerves and that "excitement" is "tickling". But elsewhere I am unable to be tickled.

When you tickle yourself, your body knows exactly where you're going to get tickled and when it's going to happen. Even if you're expecting another person to do it, you don't know the specifics... that's my guess, anyway.

I can almost tickle myself but it's not the same as when someone else does it.

What parasyte said is the official reason, but how come when there is no possible surprise, you can still tickle someone? No one knows.

I believe that when u tickle yourself your brain knows where and when you're going to tickle yourself and u have to be surprised about getting tickled