“discipline.” See note on Prov. 1:2 in ICC.
“good sense.” The Hebrew word is leb (#03820 לֵב), which is often translated “heart,” but this is one of those cases where that translation would cause confusion. In modern English, the word “heart” usually refers to emotion or passion, but that is not its meaning here. The function of the brain was unknown in biblical times, so things that we generally assign to the brain, like thinking, attitudes, understanding, and good sense, were assigned to the heart.
This is a very encouraging verse because it shows us that people who are naïve, inexperienced, or foolish, can gain good sense if they will listen to instruction and reproof. This verse should be taken to heart by parents, because in our modern world too many parents shy away from setting godly standards for their children and then not reproving the children if they fail to keep the standards. Many parents are more interested in making their children their friends than making their children godly humans, so they mistakenly fail to reprove them. Young, foolish, naïve, and inexperienced people need to be taught, reproved, and corrected to be godly. People who are charged with leading and developing others, such as parents or bosses in the workplace, cannot be afraid to reprove others, which of course is to be done in a way that is appropriate to the situation and the people involved.