I tried looking for an article on Medallion fund but haven't found it. I think it came out last year in case anyone knows what I am talking about they can post it. From my memory, the article explained how the Medallion fund operates (vaguely as much of it is proprietary) much like a casino, placing millions of small trades every day on both sides. That way market moves are somewhat irrelevant and they take a daily vig. Investments never last longer than 2 weeks.