Recently when I finished editing my latest WIP, Midnight Raynne, I found myself asking myself this very question. Is it really finished? I was pretty sure the answer was yes. At least I thought it was a yes. Now I'm not so sure.
As soon as I "finished" editing I started reading again. Not only did I start reading I started refilling my drained brain. In doing so I started noticing that I liked how the other authors described things or explained different things. I immediately started to think of my MS and thought I need to fix this or that, explain better, describe better, etc. The list goes on.
So the answer to the question is: I don't think it will ever truly be finished until it is published. Even then I'm sure I'll find things that I might have been able to elaborate on or explain differently. That's just me. I am thinking of doing one more round of edits before I send it out for review again and then I'll begin the dreaded query stage.
Your Turn -> Have you ever thought you were finished with your WIP only to realize that it was not yet completed and ready?