I always remind myself that "Done Is Better Than Perfect" whenever I think I should add some new feature to a project rather than ship it. I think the scariest thing is accepting that if you ship something people probably won't care. It's easier to continue working and not ship it under the assumption that just adding that one more thing will then make everyone love it. I don't know how it happened, but at some point…
"Perfect is the enemy of good" is another similar one you might like ;)