rats in the cellar; the reality of who we are

I love this quote from C.S. Lewis in Mere Christianity about the process of becoming true Christians:

“We begin to notice, besides our particular sinful acts, our sinfulness; begin to be alarmed not only about what we do, but about what we are. This may sound rather difficult, so I will try to make it clear from my own case. When I come to my evening prayers and try to reckon up the sins of the day, nine times out of ten the most obvious one is some sin against charity; I have sulked or snapped or sneered or snubbed or stormed. And the excuse that immediately springs to my mind is that the provocation was so sudden and unexpected: I was caught off my guard, I had not time to collect myself.  Now that may be an extenuating circumstance as regards those particular acts: they would obviously be worse if they had been deliberate and premeditated.  On the other hand, surely what a man does when he is taken off his guard is the best evidence for what sort of a man he is? Surely what pops out before the man has time to put on a disguise is the truth? If there are rats in a cellar you are most likely to see them if you go in very suddenly.  But the suddenness does not create the rats:  it only prevents them from hiding. In the same way the suddenness of the provocation does not make me an ill-tempered man: it only shows me what an ill-tempered man I am.  The rats are  always there  in the cellar, but if you go in shouting and noisily they will have taken cover before you switch on the light.”