Project motivation

The biggest motivation for me to finish a project is to get onto the next one right away. When I get about 75% into a project, I really cannot stand to work on it anymore because I have a burning urge to work on something else.  In fact the only reason I can plow through that project is because I really want to work on the other project so badly. I of course have to finish the first project because otherwise it would be a waste of time. What motivates you to complete a project?