"And you say, 'How I have hated instruction and my heart spurned reproof'"
Solomon is reminding us that there will come a day when you look back at your life and notice the significant choice points. There will be a time when you will regret the shortcuts of lust or greed or violence or lying or magic. The context around this proverb is the shortcut of lust, fornication, and adultery. But all of the shortcuts to success that wander off the path of righteousness end up in the same place – the place of regret; the place of missed opportunities; the place of emotional, spiritual, mental, and even physical consequences.
Solomon is trying to paint a vivid picture of a day five to ten to twenty years in the future when you are mired in your problems and at a place you didn't expect to be. It is then that you will think how stupid you were to do what you did. Solomon is trying to get you to see yourself in the future, either rejoicing and enjoying life or hurting and reeling from the problems.
This is the Hebrew word musar which means discipline, chastisement, correction, punishment, warning. It has the idea of instruction but instruction after having done something incorrectly. Nobody likes to mess up and even more unpleasant is the process of being punished or corrected for messing up. But if we are to grow into maturity, we must learn how to handle correction well. You can't become successful in this life without messing up from time to time. It is crucial that you learn from those mistakes. We all have to be willing to receive correction if we are going to reach our full potential. The teenager is crippled if they cannot receive correction well. We all think we are right, and yet some of those things that seemed right will be wrong. The ability to receive the chastisement, the correction, and the punishment is the key to not making the same kind of mistake the second time.
At any age we must not be closed to correction or we will be open to huge mistakes that severely wound our lives.
This is the Hebrew word tokechah which means rebuke, reproof, punishment, correction. It is a synonym for musar which Solomon uses earlier in this verse. This word seems to be more often used for verbal rebuke and correction if a distinction can be made.
The clear import of this proverb is that one should listen to those little warnings that bring you up short from what you were thinking about doing that would have been wrong because there will come a day when you will deeply regret your actions if you ignore your mentors and the boundaries of morality that you were taught.