Musar do Wyjścia 26:28

והבריח התיכון מבריח מן הקצה אל הקצה, "The central bolt will extend from one end to the other end" This is an allusion to what Maimonides in his booklet שמונה פרקים, an introduction to Avot, has described in the fourth chapter under the heading of "good deeds." Good deeds are those which do not bear a characteristic of being extreme, fanatical, intolerant. They are what we call the "golden mean." Maimonides also explains there that if a person tends to extremity in one direction and wishes to compensate for this error he should not adopt a centrist position but rather make up for the former error by exaggerating the direction he had previously spurned. After a suitable period he must then adopt a middle-of-the-road path.