I remember coming across my elderly neighbour shouting at her husband who had Parkinson's. I was in the habit of popping into her house (by her invitation) most evenings to help her put him to bed.
This particular night I was held up at work and she'd tried to get him up stairs all by herself, him trying to pull himself up on the handrail and her pushing him from behind. He fell backwards onto her, luckily only a few steps up. And she completely lost it.
It was one of the saddest things I've seen. Part shock, part exhaustion, part frustration.
Nobody should ever feel a failure because they can't always cope. They were a devoted couple, but caring for someone with a debilitating condition is ....
well you can all fill in the words. And it's much, much harder if that person is someone you love.