Why do we not want what we can/already have? (And vice versa)

[Rygar1]

Something that has been really bugging me for a long time. I'm certainly not the first, or even last to recognize this, but it's worth stating because it seems to be such a common experience with so many: WHY DO NOT WANT WHAT WE HAVE, AND WANT WHAT WE DONT HAVE.? The ramifications for this, are, in my opinion, much more profound than just a nuisance or interesting discussion. I used to experience this as a young adult when my dad would take me out to dinner and I could have anything. I'd mull it over, place my order, and then he would place his, and all a sudden, I didn't want mine and started wanting his! Can you relate?

It spilled over into other areas as well. That hot girl, yeah, you want her. But on the rare occasions she accepted your advances, what happened? I can only speak for myself, but most of the time, I all a sudden didn't want her, or at least not as much as I did at first. Why is this? Are there some biological reasons for this? Historical ramifications? I beleive this observation goes all the way back to the Buddha. Schopenhauer, I beleive, discussed this at great length, as well.