Proverbs 13:20 — "He that walketh with wise men shall be wise: but a companion of fools shall be destroyed" — states a directional principle: the people you walk with shape what you become. The Hebrew ra'a — "companion" — means to associate with, to keep company with regularly. The destruction described is not merely the result of bad advice but of sustained proximity to the wrong orientation. You absorb the character of the people you keep close.
1 Corinthians 15:33 makes the same point in the New Testament: "Be not deceived: evil communications corrupt good manners." The Greek phtheirousin ethē chrestha — "corrupt good manners" — means to destroy, to ruin good character through prolonged bad company. Paul says "be not deceived" first — the corruption is subtle enough that you can fail to notice it happening until the damage is done.
Commentary is from a charismatic Protestant perspective, drawing on KJV text and public-domain sources including Spurgeon, Andrew Murray, and Matthew Henry.