Proverbs 23:9
When exausting yourself wrestling in the mud with the pigs... Eventually you stop because you should finally realize the pig enjoys it...
It is a mere casting of pearls before swine (Matthew 7:6) to speak to such a man of high aims, righteous motives, self-sacrifice (Proverbs 9:8). He will despise the wisdom of thy words. He cannot enter into the meaning of words of wisdom; he has no appetite for them, he cannot assimilate them; and in his self-satisfied dulness he feels for them nothing but contempt.