I learned this one the hard way, and have found it again and again since: often when it's the end of the day and I'm stuck in the middle of something that seems really hard, the best thing I can do is walk away, and the next morning, it suddenly seems very easy. I call this state "being in the hole." It's a kind of can't-see-the-forest-for-the-trees thing. Always so satisfying to smash a thing in five minutes that I'd wasted an hour on the evening before.