Zeigarnik effect

"Named after Lithuanian-Soviet psychologist Bluma Zeigarnik, in psychology the Zeigarnik effect occurs when an activity that has been interrupted may be more readily recalled. It postulates that people remember unfinished or interrupted tasks better than completed tasks." (Wikipedia)

"A task left undone remains undone in two places—at the actual location of the task, and inside your head. Incomplete tasks in your head consume the energy of your attention as they gnaw at your conscience." (Getting Things Done - David Allen)