If you think other people think how you think and you can’t imagine that other people think differently then you will assume they do what you do in situations.
For example, these incel men that are oh so angry with the world because they are ugly and can’t get a girlfriend- well, irl, I see plenty of non conventionally attractive men in happy relationships because many women don’t put looks as their dealbreaker with regards potential partners. However many women would look for a partner who is kind, caring, good sense of humour, good with animals and children, intelligent, competent at running a home, clean etc which are nearly all skills and traits that can be developed and worked at but if you can’t even bear for a second to put yourself into someone else’s shoes then you’ll never see that. You’ll just look in the mirror and blame your wonky nose and get angry. Nothing changes.
Likewise if you’re looking for a woman who is beautiful, happy to stfu whilst doing all the things you want to do in life and never asks you for any kind of support then your going to be waiting a long time, even if she exists in films and tv shows.
Anecdotally, the men I know who are happiest are the ones that treat women as full human beings. The ones that make the sexist jokes, the ones that expect their wives to do it all, the ones that can’t/won’t get a girlfriend as they’re holding out for Prof. Supermodel or waiting for a coupled up woman to see the light etc all seem incredibly sad. Conversely the men I know that get stuck in to nappy changing, spending time with their families and partners and breaking out of stereotypes seem much happier.