“The man Moses was more humble than any human being on the face of the earth.” (Numbers 12:3)
Moses didn’t fool himself. He knew how good he was. He knew he stood on a level beyond any other human being. Yet he was humbled before them.
Because he knew that all that he had achieved was only with the capabilities given to him from Above. He figured that if someone else were given these same capabilities, that person would achieve as much as him.
And who knows, perhaps someone else would have used those capabilities to their fullest and achieved even more.
Rabbi Yosef Yitzchak Schneersohn, Sefer Hamaamarim 5710, pg. 236.
The humility expressed by Moses arises from Moses recognizing the greatness of G_d's quality of Love, kindness, mercy, giving above our egoistic qualities.
Moses was able to rise above our human egoistic qualities in order to connect with G_d.
He annuled his ego before G_d. This is extreme humility of the self. As this article writes: Moses was more humble than any human being on earth.
All humans have this potential within. Like Moses, we need to be willing to annul ourself, our egoistic judgements and rationale. Then G_d can provide us the same divine connection to the extent we are willing to accept the Hogher qualities.