> 90% of the code is 90% of the work. The last 10% of the code is the other 90% of the work.

Don't think I've heard that one but certainly rings true to my experience.

Reminds me of "ninety percent of the game is half mental"

I've heard it as "once you think you're 90% done, you're really halfway done."

Tangential: it's always made me wonder about teams that believe "80% effort" is optimal.