It could be either:
CPTSD - From Surviving to Thriving by Pete Walker // Trapped in the Mirror by Elan Golomb // Recovery: A Guide for Adult Children of Alcoholics by Bowden (and colleagues) //
Though now that I'm trying hard to remember which one it could have been I'm not even certain it really was one of those. Maybe it was more of an aggregated insight that I gathered from studying the subject. Either way those books can shed a lot of light on unexplainable mental blocks we have.
It's certainly in Pressfields book. He calls it 'resistance' and swears its at its strongest when you're near the finish line. That's a good observation but he doesn't go into why that could be. Those other books offer explanations to connect the dots. At least for me.
When you finish something you will probably show it to the world. So now that world will judge your talent/abilities and maybe you don't feel ready for it.
Apparently it's a common thing. I think Pressfield wrote about it in the War of Art. And it was in another book about childhood trauma I read recently, though I can't remember the title.
I could be way off. Just saying it's a possibility.