I'm curious, if the black Monday event that took place in 1987 was an 18 standard deviation move (on the conservative side) which should happen less often then 1 in the entire duration of the universe (were we just so lucky in the first say 100 years of the market to see a once in a universe event?). How can people claim to have an edge? I know risk management can limit your losses from a 1 day 18SD event, but what's to say a 5 year stretch doesn't hit an 18 SD event? How can you even have statistics on events that all possibilities aren't even known? Statistics on dice or cards are obvious as all possibilities are a given, but how can someone assume they know all possibilities in the stock market? Are edges just delusional? Real question looking for thoughtful answers.