I've had a day or two similar to that. Your subject line says it all though. Know when to quit. If it isn't working, throw in the towel and have a cold one (or two... or three...).

I've seen guys at the field having one of those days. They'll struggle with the engine or radio or something, think they have it fixed and hurry to get the plane in the air. Before you know it, the plane is spiraling into the ground.

Hope your finger is feeling better. I also stuck mine last night with the pointy end of a #11 blade. It was late, but thought I'd finish one more step. Should of known when to quit. I ended up bleeding all over the instructions for that step I had to finish.