There are none so foolish as those who underestimate their opponents due to their own inability to, err, ah, think.
The problem with philistines is that they rarely know that they are. Their simplistic efforts are followed by the self-delusion of fabricated victories. When they can’t successfully counter an argument, they cheaply attack their opponents history. And think that they’ve won.
If you think you’re winning at checkers, you may want to confirm that your opponent has not been playing chess. But you probably thought you knew that.