How much do you know about the stock market and trading? No offense but I want to know whether I am speaking with someone who has been trading for a few years and has come to this conclusion or someone who read it on a headline somewhere.
One example of some data that shows this is the SPIVA score cards. Here's a nice page that explains it and presents some of the recent results: https://www.bogleheads.org/wiki/SPIVA_scorecards
There is tons of other information if you just Google for it. When it comes to actual evidence of performance, the facts are pretty clear!
How about you? Do you have any objective data to show otherwise?