We don't like to ponder a verse like this, nor the truth of it. I think the reason is pretty obvious - who wants to think about how bad they are? Who wants to consider what they are capable of?
C.S. Lewis may be the most insightful author I've read. In this brief section from The Problem of Pain, he ponders in the manner of Jeremiah. And I mean it, he really presses in. Deeply. Richly. So much so, it will take you at least two to three times slowly reading through to get the full benefit from what he is saying here.
To what end? I leave the application to you.
Every man, not very holy or very arrogant, has to 'live up to' the outward appearance of other men: he knows there is that within him which falls far below even his most careless public behaviour, even his loosest talk. In an instant of time - while your friend hesitates for a word - what things pass through your mind?
We have never told the whole truth.
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. (paragraphing mine)