1. False Positive -- Video is brought down despite it being technically legal. Creator is mad, but YouTube suffers no more liability.
2. False Negative -- Big corporate lawyers sue YouTube for hundreds of trillions of dollars for copyright infringement. Also, these corporate lawyers would very much prefer it if you didn't believe in fair use at all. They will try to convince the court that fair use isn't a thing for weird technical reasons, and they might succeed.
So naturally the system is tuned to error on the side of generating excessive false positives. Unfortunately the enforcement side doesn't seem to understand how bad the false positive problem is and hits creators with draconian punishments for errors on YouTube's part.