Not new, Efficient Markets Hypothesis is like this. "I haven't heard of a way to make money from trading so there isn't one" is my caricature of it.

Isn't it more like: "exploitation of a market inefficiency renders the market efficient over time", or something to that effect? Or rather, (others) making money from trading is what makes it hard (for you) to make money from trading.

Sure, depends on how you encounter it. Most often on forums someone will show up wanting to hear about how to write a strategy, and they are rebuffed with "nobody would ever publish that".

I love encountering nay-sayers because it means either:

1. I am wrong and could learn something new.

2. They are wrong and their opposition fills me with defiant determination.

The difficulty comes when you view something as case 2 but it is actually case 1 and you embarrass yourself. I do this all the time.