I think the worst explanation for procrastination I've come across is that it's caused by not truly enjoying the activity that is being procrastinated upon. But if that were really the case, then the remainder of my life would be spent sitting in a chair reading useless articles online.
Other questionable explanations I've stumbled across include: being unable to bond empathetically with your future self, that the procrastinator's brain has a [insert neurotransmitter of choice] deficit, that fear of failure keeps one from starting, that too much is tackled at once, and so on.
When I try to recall what has given me the greatest sense of fulfillment in life, everything I can think of is something I worked really hard to achieve. That which contents me momentarily does not seem to coincide with that which provides overall life contentment. I don't necessarily seek happiness — I would rather have demanding work that positively impacts the world over some job that allows me to surf online all day.
What's funny is that I procrastinate only with regard to intellectual activities — not physical ones. Getting myself to exercise is no trouble at all. But prodding myself to finish a VPTree implementation... that's much more difficult. My hypothesis is that I procrastinate on those things that I was naturally good at during childhood. Academically, I was decently above average (well, at least up until college), so I never had to study. I always completed homework at the last second before it was due, and I crammed most of my test studying into the night before the exam and then promptly forgot the material as soon as I walked out of the classroom (as I'm sure many of you have noticed, this "strategy" doesn't work nearly as well in college, and it fails dramatically in grad school).
On the other hand, when it came to sports, it was pretty much a guarantee that (at least initially) I would naturally be the worst out of everyone participating. I was determined to improve though, so I developed training schedules and religiously followed them until I got the results I wanted. I think that habit has stuck with me, and I still have no trouble starting an exercise regimen.