There’s an interesting article on the Wonder Women blog about a sense of obligation being one of the main causes of procrastination.
When I was in sixth grade, I took piano lessons. Each week, I would meet with my piano teacher and tried to fake my way through the assigned pieces that I had not practiced. I hated that I had to play certain songs for a certain period of time, even though I enjoyed the piano. Finally, I convinced my mom to let me quit. From that day on, I sat and played piano for about an hour a day.