Quick answer
A parent's grief over a grown child who will not listen. The verse states it without offering a remedy.
Read both lines
Both halves say the same thing twice, which is what this book does when something needs sitting with rather than solving. What is notable is the absence of blame. The verse does not say the father failed, and it does not tell him what to do; it reports that this particular sorrow exists and is real. Proverbs is generally confident about formation, and here it is honest about the cases where formation did not take. The chapter returns to it at verse 25, which suggests the sages knew how much of a parent's life this can occupy.
What it does not mean
This is not a verdict on parents whose children went wrong. The book's own account of raising a person is a pattern rather than a guarantee, exactly as 22:6 is a pattern and not a promise, and a father in this verse is grieving rather than being indicted. Anyone reading it as evidence that a hard outcome proves bad parenting has turned a lament into an accusation.
Related: Proverbs 17:25 · Proverbs 22:6 · Proverbs 10:1
New King James Version®, Copyright © 1982, Thomas Nelson. All rights reserved. Full copyright information. Scripture provided by API.Bible.
Go Deeper
If this verse has been used to put weight on you that it was never carrying, ask about it directly.