A moderately bad man knows he is not very good: a thoroughly bad man thinks he is all right.
 C. S. Lewis, Mere Christianity (1952). copy citation

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Author C. S. Lewis
Source Mere Christianity
Topic right good
Date 1952
Language English
Reference
Note Adapted from a series of BBC radio talks made between 1942 and 1944
Weblink https://www.dacc.edu/assets/pdfs/PCM/merechristianitylewis.pdf

Context

“Remember that, as I said, the right direction leads not only to peace but to knowledge. When a man is getting better he understands more and more clearly the evil that is still left in him. When a man is getting worse he understands his own badness less and less. A moderately bad man knows he is not very good: a thoroughly bad man thinks he is all right. This is common sense, really. You understand sleep when you are awake, not while you are sleeping. You can see mistakes in arithmetic when your mind is working properly: while you are making them you cannot see them.” source