Some people are ‘cold’ by temperament; that may be a misfortune for them, but it is no more a sin than having a bad digestion is a sin; and it does not cut them out from the chance, or excuse them from the duty, of learning charity.
 C. S. Lewis, Mere Christianity (1952). copy citation

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Author C. S. Lewis
Source Mere Christianity
Topic duty sin
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

“that is, to gratify her own affectionate impulses at the expense of the child’s real happiness later on. But though natural likings should normally be encouraged, it would be quite wrong to think that the way to become charitable is to sit trying to manufacture affectionate feelings. Some people are ‘cold’ by temperament; that may be a misfortune for them, but it is no more a sin than having a bad digestion is a sin; and it does not cut them out from the chance, or excuse them from the duty, of learning charity. The rule for all of us is perfectly simple. Do not waste time bothering whether you ‘love’ your neighbour; act as if you did. As soon as we do this we find one of the great secrets. When you are behaving as if you loved someone, you will presently come to love him.” source