Pain is good, says the culture of masochism. Pain in exercising, in work, and even if it is something as petty as reading a book you don't enjoy so you can claim that you made it until the very end. Why do people do this? Probably because it benefits the status quo. Instead of looking for better games to play, people end up playing the same bullshit rigged games, with the idea that it is noble to not quit.
And so when they see someone leave such a toxic situation, they tell themselves that the person couldn't handle the job, or didn't have what it takes to stay here. Here are some more examples:
Someone hates their stressful job, but admitting that is painful—this is the sunk cost fallacy of a career path—and switching to another job is scary and confusing. So they convince themselves that this is how life is, and see anyone who quits the same job as weaklings who cannot handle the stress the same way they can
Someone wants to exercise, and they convince themselves that the more pain they feel, the better the results. They end up injuring themselves and stop any form of physical exercise for the many years to come, because they don't want to injure themselves again, not really realizing how their attitude led to that result. They do not reflect on this as a mistake, but simply think of it as how life is, that getting results necessitates pain and sometimes leads to injuries. They never consider that they could add physical activity in a softer and pleasant way
Teachers don't like their job, because it doesn't pay well and the kids are too troublesome. They could leave their job2 for something else, to improve their situation, yet they do nothing, and even derive pride for enduring their fate
Life gets a lot better when you stop looking for excuses and just get better at making changes when needed, and accepting the things you can’t change.