Proverbs 29:15 (ESV)

15 The rod and reproof give wisdom, but a child left to himself brings shame to his mother.

Notice that this proverb speaks of both “rod” and “reproof.” These are the two disciplinary measures given to parents. They should both be used with love and discernment (see Ephesians 6:4). Without such discipline a child is “left to himself,” with nothing to guide him through life but his own evil inclinations (Genesis 8:21).