Prov 20:11

“Even by his pursuits, a youth is known, etc. For whomsoever you see striving for virtues, modesty, continence, listening to the wise, and observing the commandments of God, especially humility and simplicity, know that his works are pure and right. But whomsoever you find taking a contrary course, recognize him as a man of an impure and crooked heart, and either correct and chastise him or if you cannot, avoid and shun him, lest you yourself be corrupted by him. It should not seem contrary that here the diligent youth is testified to have pure and right works, but above he said: Who can say, My heart is clean, I am pure from sin? For in this verse, he advises diligence in living rightly; in that, he dissuades from presumption of one's purity; in this, he teaches that purity and rectitude should be held as much as possible in this life; in that, he warns that the subtlety of divine examination, by which the deeds and intentions of men are judged, should always be kept in mind. Therefore, the ancient interpreters also translated that place in this way: When the just king sits on the throne of judgment, who will boast of having a pure heart? Or who will boast of being clean from sin? They also rendered the verse we are explaining more clearly, saying: A young man who is with the just will have a straight path. He who walks with the wise will be wise. Conversely, a friend of fools will become like them.”