I would say I can't believe people do/say certain things, but I have heard enough reports of them to know it's true.
eg I've read a couple of comments recently from people estranged from their parents and when they tell others, the response is 'You should make up' or 'Dont you miss them?' or 'I could never stop speaking to my Mum and Dad'. Does it not occur to these people that just because they had lovely parents, not everyone has that experience? That no one goes no contact without a very good reason?
Or asking a couple 'When are you going to have kids?' - I wouldn't ever assume everyone wants kids. I'd assume a couple will volunteer if it's on the cards, and if they don't, don't ask them?
Or people who go up to people of colour and ask to touch their hair?! Why would someone do that?!
What not uncommon things can you really not understand why anyone would say or do?