Second, the “Game Library Completion” preoccupation is another mistake, imo. I understand feeling bad about “wasting” money, but turning one’s hobby into a (monumental) task/chore isn’t gonna help that. It’ll probably just ruin that hobby.

It is really just a sunk cost fallacy. The same applies to books, movies or any other media. If you don’t enjoy it don’t finish it. Doesn’t matter how much you spent on it or invested into it in other ways. Stopping right when you don’t get anything out of it is the best time to stop that is still available (given we can’t change the past).