Environment

The manner of man's creation was such that he is drawn in his traits and actions after his friends, conducting himself in accordance with the manners of his peers. Therefore it is important to associate with righteous people and dwell in the presence of the Sages. Conversely, one must distance himself from the wicked who walk in darkness, in order that he not learn from them.

(Rambam, Mishneh Torah, Hilchos Deios 6:1)