Lewis really hits the nail on the head here. Especially in the third letter. His grasp of the human condition is shockingly accurate, and he really understands people's weaknesses. I'd be lying if I denied ever feeling like my own internal problems outweigh the world, or looking at someone and associating their lives with their faith. I can see his examples in my own experience, and I know others can, too.
I'm not saying that these feelings are inherently bad, and I don't believe Screwtape is, either. I believe the point here is that the “sin” is in focusing on them to exclusivity. Screwtape points out that these feelings will come up naturally, and that the reaction they want is to keep solely them in mind, and to block new ideas on how to look at these thoughts from occurring to the penitent. Indeed, he explicitly states in the fourth letter that blocking those new ideas is the biggest “help” Wormwood can provide.
It struck me as particularly vicious how he encouraged Wormwood to twist at petty slights. These are the easiest way to get under my skin, and I think this is true for most people. Even among our loved ones, we can be bitter about small things. My mother's in Florida right now, and I'd be lying if I didn't say I resented it a bit. I think that's just part of being human. The best I can do is make light of the situation, and joke about it instead of focusing on it and being negative.
