I saw a post on Reddit a few days ago that said something along the lines of "if you don't feel caught up, your brain is moving the goalposts on you." The post was deleted (and I'm unhappy about that), but the idea was that as we accomplish things from our to-do list, instead of letting us feel a sense of completion or satisfaction, our monkey brains instead fixate on all the tasks we _haven't_ completed yet.
I say "we" and "us." Maybe this doesn't apply to you, but it's me to a tee. (Yay #anxiety.)
I'm working on being better about seeing when I've got things done and feeling a little bit of accomplishment at that before diving into the next to-do item.