An old man once told me "Wanting something is more fun than having it".
Fieldgrade, I think you're living proof.
Nah, I don't think that's it. I have certainly never found that to be the case for me.
People who aren't happy after they get something they wanted didn't know what they really wanted. Ash doesn't really want to have a motorcycle, he just wants to shop for motorcycles. That's ok, there's nothing wrong with that.
Like when people spend a bunch of time restoring a car, then sell it after they finish. They didn't really want the car, they just wanted to restore a car.