The wise person will listen (to reprimand) and add to his wisdom (Proverbs 1:5).
One night, when Yehudah Aryeh, the future author of the Sfas Emes, was a young boy, he studied Torah the entire night and did not get to bed until shortly before dawn. Although he slept only a short while, he arose later than usual, and his grandfather, Rabbi Yitzchak Meir of Gur, sharply reprimanded him for not arising early to study. The young Yehudah Aryeh absorbed the rebuke in silence.
A friend who knew the real reason asked him: "Why didn't you explain to your grandfather why you awoke late?"
"What!" said the young Yehudah Aryeh. "And miss the opportunity to hear mussar (reprimand) from my grandfather?"
At a tender age, Yehudah Aryeh understood the profound wisdom of King Solomon, who repeatedly stresses that the wise actively pursue mussar while fools avoid it.
Mussar is to our character what water is to a plant. Abundant mussar promotes growth of character, just as water promotes the growth of a plant. Yehudah Aryeh realized that he could easily have justified his late arising, and perhaps might have even received commendation from his grandfather for his diligence. He knew, however, that while praise may be pleasant, it is not as conducive to growth as is reprimand, even though the latter may be unpleasant.