We can hardly say that the Pharisees had an accurate ‘knowledge’ of man when they pointed to the sins (the real sins) of publicans and sinners. This judgment, which separated knowledge of man from self-knowledge, was as nothing in God’s eyes. The Jew did not have a better understanding because he was able to judge the heathen. In the sphere of abstract morality this could possibly be said, but this is not Biblical morality - O man, who judgest others!
There's a quote that says, 'If you know yourself and you know your opponent, you shouldn't fear the results of 100 battles. ' Just really being prepared gives you a lot of confidence.