I've noticed that Numbers 12:3 NWT Study Bible states that Moses "was by far the meekest of all the men" on earth's surface. The footnote adds: "Or 'was very humble (mild-tempered), more so than any other man.'"
NET Bible treats Numbers 12:3 as a parenthetical statement: "(Now the man Moses was very humble, more so than any man on the face of the earth.)"
It explains that the difference in how one reads 12:3 depends on the familiar kethib-qere distinction. Furthermore, NET gives this supplemental information: "The word עָנָו (’anav) means 'humble.' The word may reflect a trustful attitude (as in Pss 25:9, 37:11), but perhaps here the idea of 'more tolerant' or 'long-suffering.' The point is that Moses is not self-assertive. God singled out Moses and used him in such a way as to show that he was a unique leader. For a suggestion that the word means 'miserable,' see C. Rogers, 'Moses: Meek or Miserable?' JETS 29 (1986): 257-63.
The Septuagint (LXX) reads: καὶ ὁ ἄνθρωπος Μωυσῆς πραΰς σφόδρα παρὰ πάντας τοὺς ἀνθρώπους τοὺς ὄντας ἐπὶ τῆς γῆς.
Targum Jonathan: "But the man Mosheh was more bowed down in his mind than all the children of men upon the face of the earth; neither cared he for their words."
Whether Moses was the meekest or the humblest (the man with a very mild disposition), despite the fact that he showed uncharacteristic long-suffering/patience, he eventually "lost it" with his people, the Hebrews (the children of Israel). We all remember when Moses struck the rock at Meribah and exclaimed, “Listen, you rebels, shall we bring water for you out of this rock?” (NRSV) So doing, he took glory for something divinely wrought by Jehovah. The consequence was that Jehovah did not permit Moses to enter the Promised Land even though Jehovah God let him see the land from a distance--and we know that Moses will be resurrected in the new earth to come: he is alive in God's eyes. However, it strikes me as somewhat ironic that Moses had exemplary mildness/meekness and humility, but even he let anger cause him to speak embittered words that resulted in deep loss: "and it went ill with Moses on their account; for they made his spirit bitter, and he spoke words that were rash" (Psalm 106:32-33 NRSV).
The account is a serious warning on the one hand reminding us to guard our spirit and always glorify Jehovah, but it's encouraging to know that the ancient spokespersons of YHWH were individuals with feelings and foibles like ours (James 5:17). Some people often get hung up on the fact that a humble person might write, "I am the most humble person on earth." It's never really bothered me that Moses might have written those words, but some scholars think the utterance is part of an editorial addition later contributed to the Pentateuch: they understand these words to be added and insist Numbers 12:3 could be parenthetical. In any event, the likely reason that 12:3 provides this detail is to let us know that Moses did not usually seek his own glory. Jehovah God (YHWH) appointed Moses as leader over Israel; the office was not gained by inappropriate ambition, but rather through divine appointment (Numbers 12:6-8). What an example that Moses set in humility, meekness or lowliness of mind. Jesus similarly was mild-tempered and lowly in heart (Matthew 5:5; 11:28), but he remained that way without taint.