This may have been O'Brian's experience as well - from what little I've read of his life apparently he was in poor health for a lot of it. As someone who's so far been comparatively lucky, but becoming an adult and seeing more of my loved ones' pains, chronic illnesses, bereavements, etc., his books have made me watch how I react and how it affects continuing interactions. For instance, he writes some very piercing things about how people's attempts to comfort their friends can go wrong. One from Reverse of the Medal:

Stephen [...] made his difficult way to Shepherd Market, carrying the parcel and at the same time managing the broad, heavy umbrella in the increasing wind. The umbrella was a mark of the younger Nathan’s sympathy: Stephen had instantly perceived the more than usually grave, attentive expression, the considerate tone, and in his present excoriated state it seemed to him that it resembled most forms of commiseration: useless, embarrassing, cumbersome and painful.