Saint Mark the Ascetic offers us an inspired answer on the importance of the way we think:
Everything good or evil begins with a thought. And gradually, nourished by other thoughts and tiny movements of the heart, it grows, takes on existence and is put into practice. People who slavishly follow their sinful thoughts are blinded by them. They see the sins to which they’re impelled by their thoughts, but are unable to see the causes of those sins, the thoughts, because of their blindness.