Ever heard of survivor bias? Let me make an example: I choose 2048 random addresses. I choose I random company on the stock market. Half of the addresses I send a email stating the stock will rise in the next month, the other half the stock will fall. After a month I check the stock and disgard the addresses where my prediction was wrong. Than I repeat the previuos steps until only one address is left. Now ask him about my expertise on the stock market.