How could Moshe Rabeinu with all his gadlus have been 'anav m'kol adam asher al pnei ha'adamah'? I have never really seen humility as being in conflict with greatness (see Netziv), but many meforshim ask this kashe. The Ohr Sameiach at the end of his Kuntres haKol Tzafuy v'haReshus Nesuna (hil tshuvah) quotes a pshat from his grandfather to answer this question. Davka because Moshe Rabeinu was so great and witnessed speaking to Hashem face to face did he feel a sense of humility. Moshe ascribed his achievements in Torah and tzidkus not to his own efforts, but to the fact that he was in a position to see the gadlus Hashem in a way that no other mortal experienced. Someone who is not blessed with that gift, a regular joe 'al pnei ha'adamah', not in shamayim speaking to Hashem, is all the more worthy for the achievements attained in spite of the obstacles of living in olam hazeh.
(See the machlokes in the Sifri what 'kol adam al pnei ha'adamah' comes to be m'ma'et, discussed by the O.S. and the Chasam Sofer al hatorah as well. This O.S. is consistant with the Meshech Chochma intro to sefer shmos that Moshe had no bechira to do wrong - l'fum tzara agra, so Moshe held someone who is engaged in struggling on avodas Hashem is greater than himself.)