It reveals a great deal about how memory works. Zeigarnik suggested that failing to complete a task creates underlying cognitive tension. This results in greater mental effort and rehearsal in order to keep the task at the forefront of awareness. Once completed, the mind is then able to let go of these efforts.

You can even use this psychological phenomenon to your advantage.

Take the first step, no matter how small. Once you've begun—but not finished—your work, you will find yourself thinking of the task until, at last, you finish it. 

This approach can not only help motivate you to finish, but it can also lead to a sense of accomplishment once you final...