The root of all sin is fear: the very deep fear that we are nothing; the compulsion, therefore, to make something of ourselves, to construct a self-flattering image of ourselves we can worship, to believe in ourselves – our fantasy selves. I think that all sins are failures in being realistic; even the simple everyday sins of the flesh, that seem to come from mere childish greed for pleasure, have their deepest origin in anxiety about whether we really matter, the anxiety that makes us desperate for self-reassurance. To sin is always to construct an illusory self that we can admire, instead of the real self we can only love. It is because we fail in realistic self-love that we fail in love for others. So sin, too, means being terrified of admitting that we have failed.
Herbert McCabe, God, Christ, and Us (New York: Continum 2005), 17-18.