One's own self is one's own friend, again one's own self is one's own enemy. One's own self is the witness of one's good and evil acts.
आत्मैव ह्यात्मनो बन्धुरात्मैव रिपुरात्मनः। आत्मैव ह्यात्मनः साक्षी कृतस्यापकृतस्य च॥