The word here translated folly, refers to foolishness which is just utterly, inexplicably silly. There are four chief words in the Hebrew Old Testament that are translated fool in our Bibles.
Do you think you are smart, are you festooned with degrees, do you have business shrewdness, do you have dress sense, a sense of the arts, and sense of fine food and drink? Are you able to say, I have intelligence and wisdom, and yet, you would embrace this world, and you would turn your back on the salvation of God? The verdict of Holy Scripture is unbelievable silliness. Nothing else can be said for it. Come, says Solomon, come to the Lord; that is the message of this fifth chapter of the book of Proverbs.