Shipping anything is a matter of knowing when it's good enough. Some people are good at deciding on the fly; others need to know ahead of time and it sounds like you need to know when to stop before you even start.

So before you begin something, decide what "done" looks like and learn to stop when you are in the "done" state. Sometimes, "done" changes. Not a problem, just understand what it means to be done and do that, no more.