Foolishness is the result of a person misusing the intelligence God has given him. A fool uses his reasoning skills to make wrong decisions. The most basic type of foolishness is denying God’s existence or saying “no” to God (Psalm 14:1). The Bible associates folly with a quick temper (Proverbs 14:16–17), perverse speech (Proverbs 19:1), and disobedience to parents (Proverbs 15:5). We are born with an innate foolishness, but discipline will help train us in wisdom (Proverbs 22:15).
Proverbs 19:3 says that foolishness is counterproductive: “A person's own folly leads to their ruin.” Jesus in Mark 7:22 uses a word which means “senselessness” and is translated “folly.” In that context Jesus describes what comes out of the heart of man and defiles him. Foolishness is one of the evidences that man has a defiled, sinful nature. Proverbs 24:9 says, “The schemes of folly are sin.” Foolishness, then, is really the breaking of God’s law, for sin is lawlessness (1 John 3:4).
Back to Proverbs 22:15 "Foolishness is bound in the heart of a child; but the rod of correction shall drive it far from him."
Children are mischievous. The way children learn right from wrong is by their parents training them. A lesson is best learned by making mistakes and being punished by those mistakes. A good paddling along with correction drives the lesson home.
The child, who is punished for doing things he has been told not to do, learns quicker than if he is just talked to. It is a natural tendency for a child to misbehave. A loving parent will spank him for bad behavior, and he will learn to do better.
There is a phrase known to many of us "spare the rod, spoil the child" is a modern-day proverb that means if a parent refuses to discipline an unruly child, that child will grow accustomed to getting his own way. He will become, in the common vernacular, a spoiled brat. The saying comes from Proverbs 13:24, “He who spares the rod hates his son, but he who loves him is careful to discipline him.” The Lord uses discipline to reveal our sin to us. This is also how parents reveal the truth of our need for a Savior to their children. When a child does not feel the consequence of his sin, he will not understand that sin requires punishment. The Lord provides a way to salvation and forgiveness through Jesus, but that means little to those who do not see their sin.
Furthermore, correction shows us that we are not above reproach and that we are accountable for our actions.
When it comes to our eternal destiny, one is either a fool, meaning he rejects the gospel of Christ, or one is wise, meaning he believes in Christ and commits his life to Him (see Matthew 7:24–27). The believer discovers that the gospel—what he thought was foolishness—is in reality the wisdom of God providing him eternal salvation.