With all due respect, rabbi, I don't think you could possibly give me a satisfying answer to the following question.
In the Torah it says, "And Moses was exceedingly humble, more than any man on the face of the earth". Very nice compliment, but who wrote this verse? Moses himself! Is that called humility?!
Before I answer your question, allow me to make it even stronger. It also says in the Torah, "Moses spoke face to face with G‑d", "No man like Moses ever lived" and countless other similar praises. How could Moses write all this if he is indeed humble?
The question is based on a misunderstanding of what humility is. If being humble means thinking of yourself as a good-for-nothing scumbag then your question is a good one. But that's not humility. That's low self-esteem, which is the opposite of humility.
Truly humble people recognize their own talents and achievements. But they don't take credit for them. They feel that their talents are gifts from G‑d. They truly believe that their achievements are only due to the opportunities that came their way. No matter how successful, popular and gifted they may be, it won't go to their head, because they feel that it isn't their own accomplishment.
Moses was more humble than any man on the face of the earth. He was fully aware of the amazing feats that he had achieved. He took the Israelites out of Egypt, led them through the desert, spoke to G‑d on Mount Sinai for forty days and forty nights. No other human in history had reached such heights, and Moses knew it. But he truly believed that his greatness was a Divine gift, and had somebody else been given his opportunities they would have utilized them better than he did. He would look at the simplest of people and think, "If he was in my shoes, he would have been a better Moses than me."
To see yourself as worthless is not humility; that's just being ungrateful. G‑d has blessed each one of us with unique qualities, and we should be aware of that. In fact, only when we are aware of our self-worth can we be humble. We are humbled when we ask ourselves "I have been given the potential for greatness - have I used this gift?"