I have a simple rule when it comes to deciding if a design is finished: would I put it in my portfolio?
I used to be pretty good at convincing myself my latest work was "good enough"- deadlines, boredom and difficulty definitely encourage such rationalization. I used to ignore that voice in the back of my mind that said it just wasn't there yet. Since I started trusting my gut instinct, I've found myself asking "what was I thinking?" a lot less often.
Everyone will tell you "bad isn't the enemy of good, perfection is"- and that's definitely true. But all to often, it's used as a cop-out. An excuse to release something that's not quite up to par.
So, next time you're wondering if you're done- is it good enough to land you your next gig? Are proud enough to put it in your portfolio? And, of course- remember to be honest.