No offense dude but you don't know enough to know that you don't know what you are talking about. A stop loss guarantees a closed trade, not a price. So pre-trade, you still have an undefined loss.Traders (most or otherwise) do what they do and neither you, me or anyone else knows with any certainty what most do.
Meanwhile saying a P&L is unknown with a closed trade is just ignorant.
BTW ever heard of a thing called limit order?
Think about an active equity mutual fund or a hedge fund with a position in a stock. If the fund size is $1B and they hold, on average, 50 positions, you're talking about an average of $20MM per name. That can represent more than 5-10% of the average daily $ volume of the stock. Exiting on a stop loss would create a huge loss for the fund -- because they would not be able to fill at a reasonable price (it would create a shock, which would push the price much further down -- especially with HFTs and short momo trading kicking in).
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