It doesn't, really.
I'm not trying to be obtuse, but we looked after him and loved him as well as we could, as flawed human beings ourselves.
Mum has been far gentler with Grandad and his infirmities than she ever has been with Dad. I saw that she worked hard for him and how much she cared. And how she made time for all the little things - listening, cheering him up, making him lunch he liked, doing all his washing and ironing even when he had "accidents". And then the bigger things - seeing him every day in hospital, spoon-feeding him, holding his hand, massaging his feet, talking talking talking about the old times and hoping some is getting through and comforting him.
Grandad did not need to write that letter to Mum. She's not perfect, but on the occasions she called him a stupid old git or a moaning bastard it was only behind our closed front door
The next day she was back looking after him in his house or the hospital or the nursing home. Still, if I forwarded it on to her she would feel guilty.
As I say, just because it doesn't fit my experience, doesn't mean I'm denigrating it.