When someones says she knows what works

It’s funny when you talk with gurus and they say… believe me, I’ve been in this business for a long time and I know what works and what doesn’t.
What a fallacy. So, everybody knows what works? In that case, it’d be a lot of billionaires out there, right?
Nobody can know accurately what works. That’s not possible. You can have a rough idea of what should work, but you will never be 100% sure of something.
If you want to be sure, you better test. If not, in the end you have the same likelihood as throwing a coin.
Go down to earth and prove your rightness. Gurus stay at home.