The book of Proverbs says you should not answer a fool according to his folly. That’s because that would be a foolish way to respond, and then you would be no better than the fool.
It then immediately contradicts itself and says you should answer a fool according to his folly. Because if you don’t, the fool will go on thinking he’s wise.
There’s also another proverb a few chapters earlier that says you should not answer a fool according to his folly. This time, it’s for the simple reason that you shouldn’t speak to fools at all, because they wouldn’t listen to your advice anyway. If that’s true, that second proverb is wrong in assuming that you can talk to a fool and show him how unwise he is.