Procrastination might be caused by lack of confidence in achiveving.

[dor]

Procrastinator’s anguish: he knows that the job has to get done, that putting it off just makes it harder and the worry worse. And yet...
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His research contradicts one major theory, which is that procrastinators suffer from anxiety and so have a harder time facing a difficult task.

Steel looked at the literature and found that statistically there's very little correlation between anxiety and a tendency to procrastinate.

The same with the flattering idea that procrastinators are also perfectionists, people who care so much about doing it right that they can't bear to get started. Again, Steel found no correlation.

What he did find is that procrastinators are less confident that they can handle a given task. They're also more impulsive and less conscientious overall.

"Whether you believe you can or you believe you can't, you're right," Steel says."Some of these old wives' tales bear out. People who believe they can are less likely to procrastinate."

[Dani]

A significant part of it also is having no overriding purpose.

If I have no current goals, or goals I am not really interested in, then I procrastinate like there is no tomorrow.

Once I find a significant goal, and get myself on purpose for it. I find all of the time sinks in my life games, movies, girls etc. Just fall away and I almost totally stop procrastinating.

When you have a purpose you can clearly visualise it boosts your confidence. When you lack purpose you rarely do anything at the 100% level and your confidence suffers as a result.

I would agree that confidence is a major part. Lacking goals cannot be discounted though.

[Liara Covert]

I know an individual who appears lazy and unfocused but his insecurity actually explains he is afraid of success. This person is definitely not a perfectionist. However, he likes to make it appear like he has things under control. This individual's personality and behavior don't exactly fit the study results in question. Of course, it can be dangerous to generalize any theory. Its usually possible to find exceptions to every rule!

[Erock]

My view on why we tend to procrastinate big hard projects (from a consciousness point of view) is that the ego knows that it will need to be silent temporarily so we can enter that creative zone and complete the project. Obviously it does not like that and will make up any excuse to prevent it.

Erock