These argument must be taken with a grain of salt. The truth is you don't know how many independent random investing they actually make. The classic argument is

These argument must be taken with a grain of salt. The truth is you don't know how many independent random investing they actually make. The classic argument is that given more than 1000 people there will be someone with a perfect score in 10 coin toss. But the reality is that some investor only tossed 5 times(big bet, long term investment), while some others tossed 100 times(short term, lots of smaller trading). It's much easier to say to a PE fund which only makes a deal every 2 years that its success is pure luck, than say the same thing to a high frequency trading firm who trades every second.