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.
From Mere Christianity by C S Lewis