"You cannot have too high an opinion of yourself because the world will always strive to correct you."

via Ask Eric: Maynard G. Krebs: "You cannot have too high an opinion of yourself because the world will always strive to correct you. The only thing most people hate more than success is self-confidence-a warning signal that you might be a success soon. This is not what they teach you in Sunday School, but it happens to be true: at any evidence that you might be a success, the envious will do every-thing in their power to destroy you. Therefore, there is no chance at all that a high self-esteem will go unchallenged; it will be challenged on all sides, daily. On the other hand, if you have a low opinion of yourself, nobody will ever correct it. You will have it for life unless you correct it yourself... 

Rabbi Hillel put it all in a nutshell 2000 years ago: "If I am not for myself, who will be for me? If I am only for myself, what am I? And if not now, when?""