You are right. It is trained on a lot of data, more than what a person van read in many lifetimes, but not all.

In fact it will be interesting how much more it would be at copywriting for specific feilds once it can train on that data. I imagine an LLM trained on all that dusty text in courthouse basements would become a much better paralegal (won't be a lawyer I'm afraid) than vanilla chatGPT