From Maria Popova:
Our brain appears to be wired to nag about unfinished to-do list items as uncompleted tasks and unmet goals continue to pop up into our minds. This is called the Zeigarnik effect and explains phenomena like earworms — when you hear only a portion of song, the song is likely to run through your mind at odd intervals as your brain struggles to finish it. Originally, the Zeigarnik effect was believed to be the brain’s way of ensuring goals are eventually accomplished, by prodding you into urgency until they are. But recent research has shed new light on the relationship between the conscious and the unconscious in our cognitive to-do lists.
[It] turns out that the Zeigarnik effect is not, as was assumed for decades, a reminder that continues unabated until the task gets done. The persistence of distracting thoughts is not an indication that the unconscious is working to finish the task. Nor is it the unconscious nagging the conscious mind to finish the task right away. Instead, the unconscious is asking the conscious mind to make a plan. The unconscious mind apparently can’t do this on its own, so it nags the conscious mind to make a plan with specifics like time, place, and opportunity. Once the plan is formed, the unconscious can stop nagging the conscious mind with reminders.”
The moral, then? Unless you are Woody Guthrie, keep your to-do list to a few very specific, actionable, non-conflicting items, then go fly your kite in peace.