The man makes a distinction between honest criticism and hollow noise

A friend's honest wound heals you. A stranger's flattery poisons you sweetly. The wise man learns to tell which is which, and listens only to the first.

Two failures sit on either side of this. The fragile man hears all criticism as attack and learns nothing. The vain man swallows all praise as gospel and learns worse than nothing. The wise man runs both through a single filter: is it true, and does this person want my good? If the answer is yes, he keeps the hard word even when it stings, and he thanks the man who paid the social cost to say it. Flattery is cheap and plentiful. Honest correction is rare and worth more than gold.