This is the first and most important item to remember. Some of the tasks your boss sends across your desk will never get crossed off. Accept that some of the brilliant ideas you’ve had while in the shower will never get completed. And some of the promises you made will get broken.
Forgive yourself. And move on.
That is something we all deal with — it is difficult to know that something is not complete, but unless you shed yourself of the guilt associated with it, it begins to affect your current work. What’s done is done.