Greed

I think it's human nature that once you have something, you want a little bit more.  A little bit more money, a bigger house, a bigger car, and on down the line.  I would guess that this greed is built-in, or perhaps it's also exacerbated by cultural conditions.

I think greed is unknowingly applied to a lot of fitness and health programs.  If you do well, then you want to do even better.  If you reach a goal, then it's time to set a bigger one.  All with the promise of future happiness awaiting.

Certainly, I am guilty of this myself.  I can't count how many times I've said that when I get to such-and-such weight or body composition that I would be happy.  And whenever I've reached these goals, they did make me happy - temporarily.  Then the hedonic treadmill will begin again, and it would be time for new objectives.

It's important to differentiate between greed and challenges.  Done in a healthful way, challenges can be a great way to motivate.  Greed, on the other hand, is the darker side of ambition.  It's more of a succeed at all costs attitude - regardless of health impacts.

The emotions of greed can easily lead to overtraining.  There can be mental hurdles to putting in "easy" workouts - the concept of laziness enters the picture.  After all, doesn't "working out" imply that there's work involved? 

Historically, I don't think hunter-gatherers were very greedy in terms of their exercise.  Their "exercise" was physical movement for the purposes of food procurement.  I don't think they would have intentionally keep exercising once they had acquired sufficient food.  Maybe showing off in a tribal dance, perhaps, but I doubt anyone was repeatedly lifting rocks for fun.