Comment by pier25

Maybe the projects weren't 90% done but more like 50% and you stopped simply because you rely on motivation rather than discipline.

Things only get more difficult as any project progresses so it's only natural that you will need more effort to reach the end. Novelty is long gone since the project started and now only hard work remains.

Plenty of people talk about this. Some people call it the valley of despair, pit of failure, etc. There's even a book called The Dip.

Personally I'd say the last 10% (real 10% not imagined) is rarely when people quit a project.