Things like 'the cost of doing business' didn't make full sense to me until I was running a small one. I agree some lessons aren't easily taught unless you have skin in the game or some kind of first hand experience.

As a loose analogy paper trading can work great as practice(and if done right is supposed to help with this). Yet when u apply your system and stuff goes sideways, you're sweating and emotionally(as well as financially) impacted for real now, not just on paper. Those losses are real and paper trading would never 'hurt' like that.