Rambam (De'os 1:5) A person who carefully [examines] his [behavior],1 and therefore deviates slightly from the mean2 to either side is called pious.What is implied?4 One who shuns pride5 and turns to the other extreme6 and carries himself lowly is called pious. This is the quality of piety.7 However, if he separates himself [from pride] only to the extent that he reaches the mean and displays humility, he is called wise. This is the quality of wisdom.8 The same applies with regard to other character traits.
Rambam (De'os 2:3) There are temperaments with regard to which a man is forbidden to follow the middle path. He should move away from one extreme and adopt the other. Among these is arrogance. If a man is only humble, he is not following a good path. Rather, he must hold himself lowly and his spirit very unassuming. That is why Numbers 12:3 describes our teacher Moses as "very humble" and not simply "humble". Therefore, our Sages directed: "Hold oneself very, very lowly." Also, they declared: "Whoever is arrogant is as if he denied God's presence, as implied by Deuteronomy 8:14: 'And your heart will be haughty and you will forget God, your Lord.' Furthermore, they said: "Whoever is arrogant should be placed under a ban of ostracism. This applies even if he is only somewhat arrogant."
This contradiction was noted by the Lechem Mishna
Avodas HaMelech (01:05) ואם נתרחק עד האמצע בלבד ויהיה עניו נקרא חכם וזו היא מדת חכמה. ועי' לח"מ שתמה ע"ז טובא דהא בפרק שאח"ז כתב רבינו שאסור לנהוג במדת הענוה במדה בינונית ועוד תמיהות, ועי' מ"ש ישוב הדברים לקמן בפ"ב ה"ג.