How do you decide when a project is done vs when youre just tired of it?

I keep getting to like 85% finished on projects and then losing steam. The garment is wearable but I havent done the final pressing, or the hem is pinned but not sewn, or I skipped the hook and eye at the top of the zipper. Then it sits in the pile for weeks. Anyone else deal with this? How do you push through that last stretch?