Revenge also comes into play. If you are angry about being assigned a certain task, put it off as long as possible. Most procrastinators get routine work completed without much trouble. They have to. It's the project, the creative job, or the unusual or big job that gets postponed.
Psychologists recommend determining how much time is available after routine work is done.
That's the amount of time available for projects. Learning to devote a half hour without stopping is considered good. It's not easy to change habits. Most people get discouraged with their progress. Working at it consciously makes people less prone to postpone.