Mark 7:20-23 (Jesus speaking):
What comes out of a person is what defiles him. For from within, out of the heart of man, come evil thoughts, sexual immorality, theft, murder, adultery, coveting, wickedness, deceit, sensuality, envy, slander, pride, foolishness. All these evil things come from within, and they defile a person.
The older I get and the better I get to know myself, the more I see this is true.