Lack of confidence, sometimes alternating with unrealistic dreams of heroic success, often leads to procrastination, and many studies suggest that procrastinators are self-handicappers: rather than risk failure, they prefer to create conditions that make success impossible, a reflex that of course creates a vicious cycle.
I do think that procrastination evolved in humans for good reasons. If you're trying to stay alive as a human being on the savanna 20,000 years ago, worrying about what's right behind that bush is a lot more important than worrying about what might happen three weeks from now.
One of the problems that exacerbates procrastination is the feeling that you have lots of different things to do and no clear sense of which matter more, when they should be done, etc.
I think there is clearly a connection between free time and procrastination. The more you have of the former, all things being equal, the more likely you are to procrastinate.
The essence of procrastination lies in not doing what you think you should be doing, a mental contortion that surely accounts for the great psychic toll the habit takes on people. This is the perplexing thing about procrastination: although it seems to involve avoiding unpleasant tasks, indulging in it generally doesn't make people happy.
Academics, who work for long periods in a self-directed fashion, may be especially prone to putting things off: surveys suggest that the vast majority of college students procrastinate, and articles in the literature of procrastination often allude to the author's own problems with finishing the piece.
Addictive behavior is kind of the inverse of procrastination: procrastination is about not being able to do what you want to do, addiction about not being able to not do what you don't want to do (drink, use drugs, etc.)
Procrastination also can be a way of self-handicapping: if you don't do a great job, you can always say to yourself, "If I'd only started sooner, I'd have been able to produce something excellent."
There are lots of people who believe there may be at least some genetic component to procrastination, and even if there isn't, it seems to be the case that procrastination habits are often set relatively early in life (that's certainly the case with me). But I also think that there's lots of evidence that external tools can help quite a bit in getting people to stop procrastinating.
