Why do we do what we do?
Why do some of us have the impulse to prove something wrong or try to do something that is pointed out to be impossible?
For example, what if I told you that:

It is said to be impossible to lick your elbow.

...I'll let that sink in.

Over 75% of people who read this will probably try to lick thier elbow.
Is this due to the fact that the notion of licking our elbow has never crossed our minds and becomes a intrigueing thought that causes us to experament?
Or are come people just plain stupid?
Or is it something more deep and psychological?
Any thoughts?