The Zeigarnik Effect, as defined by Cal Newport in the amazing to contemplate and difficult to apply Deep Work, is as follows:

This effect, which is named for the experimental work of the early-twentieth-century psychologist Bluma Zeigarnik, describes the ability of incomplete tasks to dominate our attention.  It tells us that if you simply stop whatever you are doing at five p.m. and declare, “I’m done with work until tomorrow,” you’ll likely struggle to keep your mind clear of professional issues, as the many obligations left unresolved in your mind will, as in Bluma Zeigarnik’s experiments, keep battling for your attention throughout the evening (a battle that they’ll often win).  152 – 153

It strikes me that David Allen’s entire Getting Things Done system is an effort to battle this particular effect.  He encourages us to write things down in a trusted system so that they do not linger in our minds.  Cal Newport also presents some nice fortifications against malingering tasks, but I won’t summarize them for you because I recommend you read Deep Work in its entirety.