Ever tried to tickle yourself and succeeded?

The body literally has a fail safe that makes it impossible to actually tickle yourself because the laughter from a tickle is the result of a type of panic response. You wont make yourself panic.

I get the sensation of the tickle, but won't laugh from it.

I've tried because I read somewhere you can't and I did not succeed

You can't, it's physically impossible. Your body knows it's you and therefore doesn't react in a spasmic way like that.

It's easy, the roof of your mouth

I've successfully hit my funny bone in my knees