An email sits in your drafts, written three separate times and never sent. It costs a small amount of energy every time it crosses your mind, which is considerably more often than the task itself deserves.
Unfinished business isn't heavy because it's difficult. It's heavy because it stays open, and open things keep a light burning somewhere in the back of your head.
Consciously is the word doing the work. Picking one to close on purpose this week, rather than waiting to be forced into it by a deadline or a phone call you didn't want.