I don’t really believe people who say “money is just paper” and act like losing it doesn’t matter.

There’s a high chance it’s cope. Either for the feed, or to protect themselves from the feeling.
Money isn’t the goal, but it is energy. It’s time, options, safety, freedom to make mistakes, freedom to say no. Pretending it’s irrelevant doesn’t make you evolved, it usually just makes you reckless.
The “money doesn’t matter” line almost always comes from two places:
People who don’t have it and need a story to feel okay.
Or people who have plenty and like playing the enlightened guru.
A healthier approach is just respect.
Same as relationships. If you pretend you don’t care, you start treating it badly. If you treat it with respect, you make better decisions and you stop sabotaging yourself to look tough.
In markets, this matters more than any thesis.
If you don’t respect your capital, the market will teach you. Repeatedly.