Know when to keep trying. And know when to cut your losses and call it a day. If you're tiring yourself out and not getting anywhere, if what you're doing brings you absolutely no joy, and if you can't see how your efforts are going to get you to the bigger picture, quit. Focus you efforts on the things that are worthwhile to you. Don't waste your time on the others.
[If you want to start with this series from the beginning, click here. You can check out all the other 31-dayers here.]