There was an interview with Paul Tudor Jones in Market Wizards who worked with a floor trader who said that is it a common pit practice to dump positions when a lot of small retail orders are coming in. (I can't remember the exact words but it was sort of like that.) Then the same sort of thing was explained in John Carter's book "Mastering the Trade". I guess they have to sell when they can so they do when a bunch of orders come in. I also suspect however that it may partly be due to what I call "the culture and mentality of the markets". They simply assume that the small retail customers are usually wrong so they'll fade their moves. Alan Farley in The Master Swing Trader, David Nassar in Market Evaluation and Analysis for Swing Trading and John Carter in Mastering the Trade all insist on being "anticipitory" rather than reacting. In other words, they say you should try to position yourself ahead of a breakout, not after it. This is partly because you may not get filled when the breakout occurs or you may get a bad fill right at the top of the move. Well, that's me guessing anyway.