Confessing sin, as good and necessary as it is, is also inadequate, as C.S. Lewis warns in this passage from The Problem of Pain.
We may confess ugly facts—the meanest cowardice or the shabbiest and most prosaic impurity—but the tone is false. The very act of confessing—an infinitesimally hypocritical glance—a dash of humour—all this contrives to dissociate the facts from your very self. No one could guess how familiar and, in a sense, congenial to your soul these things were, how much of a piece with all the rest: down there, in the dreaming inner warmth, they struck no such discordant note, were not nearly so odd and detachable from the rest of you, as they seem when they are turned into words. We imply, and often believe, that habitual vices are exceptional single acts, and make the opposite mistake about our virtues—like the bad tennis player who calls his normal form his “bad days” and mistakes his rare successes for his normal. I do not think it is our fault that we cannot tell the real truth about ourselves; the persistent, life-long, inner murmur of spite, jealousy, prurience, greed and self complacence, simply will not go into words. But the important thing is that we should not mistake our inevitably limited utterances for a full account of the worst that is inside.†
† C.S. Lewis in The C.S. Lewis Bible, NRSV (New York: HarperOne, 2010), 136.