'You can never get enough of what you don't really need.' Though this profound personal-growth axiom usually refers to things like "others' approval" (you really need your own), it is equally applicable to productivity. Many people are trying but can never work hard enough, because working hard is not really what they need. They need to simply be doing, in a careful and concerned way, without care or concern. Haven't you noticed that working hard at the right thing is not hard work?
— David Allen, Ready for Anything (lead-in to chapter 16, "Working hard enough is impossible")
I mentioned this aphorism to achaosofkittens yesterday, and he thought it sounded wrong on its face, because it seemed to be saying that there's no way to be satisfied with a finite amount of something you want but don't need. As a counterexample, he suggested sex: people are usually satisfied right after they've had it. But my answer was that it's usually just a temporary, physiological satisfaction, and the desire comes back quickly for people who are overly preoccupied with it. Similarly, take someone who is addicted to shopping -- they are satisfied right after buying something, but it doesn't last.
"Need" and "want" are fairly relative terms, though. Do I really "need" a job? Friends? Education? It depends. So I think need vs. want is the wrong distinction to apply to this aphorism. "Need/want" vs. "*think* I need/want" seems more like it to me.
So if you want X, and doing Y will get you X, but you *think* doing Z will get you X (and it won't), the problem occurs if you keep on doing Z anyway. There are various reasons this might happen: maybe you think you haven't done Z enough yet, or maybe Z has side effects that you like which distract you from thinking about X, or maybe you're dogmatically convinced that Z must bring about X. Or maybe, and this is probably the most unfortunate case, you don't realize your goal is X in the first place.