My son, heed the discipline (mussar) of your father, And do not forsake the instruction (Torah) of your mother;
הַדֶּרֶךְ הַיְשָׁרָה הִיא מִדָּה בֵּינוֹנִית שֶׁבְּכָל דֵּעָה וְדֵעָה מִכָּל הַדֵּעוֹת שֶׁיֵּשׁ לוֹ לָאָדָם. וְהִיא הַדֵּעָה שֶׁהִיא רְחוֹקָה מִשְּׁתֵּי הַקְּצָווֹת רִחוּק שָׁוֶה וְאֵינָהּ קְרוֹבָה לֹא לָזוֹ וְלֹא לָזוֹ. לְפִיכָךְ צִוּוּ חֲכָמִים הָרִאשׁוֹנִים שֶׁיְּהֵא אָדָם שָׁם דֵּעוֹתָיו תָּמִיד וּמְשַׁעֵר אוֹתָם וּמְכַוִּן אוֹתָם בַּדֶּרֶךְ הָאֶמְצָעִית כְּדֵי שֶׁיְּהֵא שָׁלֵם בְּגוּפוֹ.
The straight path is the mean disposition found in each and every tendency of all the human tendencies. Such tendency is removed from both extremes an equal distance, and is not nearer to one than to the other. Therefore have the wise men of yore commanded that man should ever review his tendencies, (Sotah, 5b. C.) estimate them, and direct them toward the middle-path so that he will be sound in body.
And how may their cure be? He who is of a hot temperment should be taught to demean himself this wise: If he be smitten and cursed, he must not feel the insult at all. and follow this way a long time until anger will be completely rooted out from his heart. And he who was arrogant should accustom himself to a life of extreme self-abasement by occupying the lowermost seat of everybody, and dress in such rags which shame those that wear them, and do such in like matters until the haughtiness of his heart will be rooted out of him, when he will return to the middle-way, which is the good way. But when he will return to the middle-way he should follow it throughout his lifetime. And this line he should follow in all the rest of his tendencies; if he had distanced himself to the extreme point of one he should remove himself to the extreme end of the other and follow it up a long time until he may return to the good way, which is the middle-standard in each and every tendency.
...A philosopher asked Rabbi Hoshayah: He said to him, if God so loves circumcision why did he not give it to Adam. He said to him, why does that man (you) shave the corners of your head and leave the corners of your beard? He said to him because it grew with me in folly. He said to him: if so you should blind your eyes, lop off your hand, and sever you legs since they grew with in follow. He said to him: To these words we have come wonder. He said to him: Anything created in the first six days, needs further actions, for example mustard seeds need sweetening, peas needs sweetening, wheat needs grinding, even humans need fixing.
The Midrash teaches (Bereshit Rabbah 11:6), “Everything that came into being during the first six days of creation requires improvement – for example, the mustard seed needs to be sweetened … also humanity needs rectification.” Our world is a world of transformation. When we are improving and refining ourselves, we are in concert with the Divine plan – fulfilling our purpose for existing in this world … Not only is the human being created for this purpose, but he is also given the ability and capacity to attain this supreme goal.
There also developed a second, "maximalist," trend of Mussar yeshivot, in the so-called "Nowardok style." Its proponent, Joseph Josel, the "old man of Nowardok" (Novogrudok), applied a deeper psychological approach. This not only included many hours devoted to the study of the Mussar texts, employing if possible a more plaintive melody, with less light, but the student would also be taught to discipline himself by a series of peules af … ("actions to …"). Such actions were calculated to subdue his natural instincts of vanity, economic calculation, or love of material goods. A student, for example, might be ordered to go to a drug store and ask for something inappropriate, such as nails, to mingle with well-dressed people in rags, or to enter a train without a coin in his purse. By the Nowardok method, a man not only trained himself to subdue his animal and social nature, but also to check if he did so in complete emotional depth.