According to the New Jerome Biblical Commentary, (with two forwards written by Carlo Maria Cardinal Martini, SJ and Augustin Cardinal Bea, SJ) this verse may be properly understood from verses 1 - 19. The theme may be said to be words for “Prudence in One’s Affairs”. The commentary speaks these verses in regard to “tradition of the elders”: “The wisdom that was handed down from one generation to the next.”
I believe it is safe to say this points to the apostolic succession which preserves the Sacred Deposit of Faith, by which - we may know (Prudence) what to obtain and what to avoid.
You say and ask, “But since we are to help everyone, what are we to do if we encounter a foolish person who is also lonely and in need of companionship? Or will a foolish person always have foolish friends, so they don’t need our companionship?”
I answer, consider the words of the Seraphic Doctor, Bonaventure, in his commentary on Ecclesiastes - “The fourth kind refers to prelates (spiritual, and more so these days temporal). First, in their teaching when the text says: A time to keep silence and a time to teach (Eccl 3:7), for a person must first learn and later teach. Sirach 18:19 reads:’ Learn before you speak.’ Sirach 32:9 advises: ‘Hear in silence.’”
Finally, a phrase I have read from the Magisterium recently is “theology on the knees”