from the guys, i hang with doing that volume daily on automation... they are revert to mean, across tons and tons and tons of stocks (law of numbers) in the big picture, it is more like they are market making (which a few do as well, on very short term conditions...) a few others, i know are excellent traders in a select few stocks and THEY bang away on monster size, scalping. mksummny, for instance. these are the guys i chat with who absolutely astonish me with their "darkside/manual" trading ability- scalping! wtg!