I came across Tim Berry's nostalgic write-up of Adam Osborne and was left in awe at the vision and practical thinking Osborne exhibited so many years ago. This quote of his is a keeper -
"Adequate is good enough."
At our company, this rule is embodied in a cat statuette floating around the development workspace that holds a sign reading "80/20" (named for the Pareto Principle). The cat serves to remind us all - product management, sales, service and developers alike - to separate the wheat from the chaff. It's all too easy to get carried away on the finishing touches to your product, paper or even to an email or proposal you're writing - but if you're at the 80% level (or in Osborne-speak, when it's adequate) - you're readier than you'll ever be.
Be brave, ship, and you'll learn so much more from your product's interaction with the real world outside than you ever will from those finishing touches you're dying to add at the last minute.