Uncompleted tasks and unmet goals tend to pop into one’s mind – this is called the Zeigarnik effect. Completing the task (or making a plan to do so, the more specific the better) will cause your unconscious to stop nagging you with reminders.

That's the basis of the book Getting Things Done. He recommends doing all things that take two minutes immediately, but otherwise having an organized method off dealing with all issues, where it's all written down and planned, so no nagging is required. Everything is handled, and you know it is handled, so your brain doesn't have to nag you about it.