The Zeigarnik Effect

This effect describes our tendency to remember incomplete or interrupted tasks better than completed tasks. Each unfinished task takes up some of your attention, splitting your focus. It also interferes with your sleep.

What you can do about it:

Our brains are hard-wired to keep us thinking about our unfinished tasks until we’ve completed them.
This psychological phenomenon is called the Zeigarnik Effect.

Starting but not completing too many projects puts people at risk of the Zeigarnik effect, which states that people are better at remembering unfinished tasks than completed ones.