"Happy endings and how do you earn them?"
Interesting question, but I'm wondering if all endings have to be earned. Entropy is always with us, so sad or inconclusive endings can also be an easy option.
One of the A.S. Byatt books in the Virgin in the Garden series ended with people sitting quietly in a room, and it had a strong impact. (This is from memory, and it's literally the only thing I remember from the book.) How did she get away with that?
Any other endings that would go in the "I can't believe that worked" category?