I have three reasons why.

One, I have a friend who, a few weeks ago, posted on her Facebook status update: Got a super shweet bonus. Yesterday she posted: wonder how long it will take me to find a new job. Obviously, the bonus was not the be all and end all.

And you wrote about the kid and the skateboard. Now, take a kid with no interest in skateboarding and offer him (or her) money to learn the trick, make it an intermediate or advanced trick, if the kid really has zero interest in skateboarding, you could offer them $1000, $2000 or more and he/she will never ever earn it. Skateboarding is hard, you fall off, you get scraped up. If you want to learn, all that is part of the process, if you don't, you'll give up.

And, I"m getting my master's in education. It's pretty much what all the educational research says (despite ever more new policies to the contrary) - kids do best (and adults) when they are motivated by internal stimulus and curiosity and will retain that knowledge much longer. They want to learn, they are motivated to learn, they will learn. Otherwise, they just keep it long enough to get the 'A' or the award and out it goes. That's why Jay Leno can stop people on the street and make them look like idiots. They had no interest in the first twelve presidents of the US to begin with.