We've all met this guy. He is the know-it-all, the blowhard, the dude who talks uninvited about himself and won't shut up. He is a rude, self-consumed, arrogant person who is never content to have any conversation that isn't about himself. He'll tell you how he would handle your life, without you ever asking for his input.
Proverbs says such a person is hopeless. He is worse than a fool, and fools should be avoided! In fact, given a choice between a wise-acre boor like this and a fool, take the fool... you'll be better off! That's how bad self-wise people can be.
I am afraid the world is cranking these men out now by the trainload. Many people over value their personal insight. And it is detrimental to society. Self-made men draw their own blueprints, unaware of fatal design flaws. That is not a good thing. Human insight, flawed by sin, inevitably fosters serious defects into self-wise men.