"Bake cookies only as long as you enjoy the process"
That's one way Helen Isolde, How to Have A Perfect Christmas says we can have a perfect Christmas. Seems like good advice for just about anything we're working on. As soon as we lose the joy of something, we should stop. Pay attention to how we are feeling and ask why everything's just gone emotionally downward.
It could be that we're tired and need a break; it could be that we're irritated because we'd rather be doing something else; perhaps it's that we're feeling pressured by expectations (real or perceived) and we don't like that feeling of being out of control.
It's okay to Stop. Quit. Reverse. Rest. Reschedule if necessary. If you need permission, give it to yourself ... you can, you know! Turn off the stove and come back later.