After three consecutive days of losses, Simon fell into panic and made a mistake in his new transaction. He instructed the dealer to "buy 800 shares of GS on the market", but he was intended to sell 800 shares. He realized this mistake immediately but the transaction has been made. To correct the position to where he wanted, Simon instructed the dealer to "sell 1600 shares of GS on the market" . This mistake wasted him $200 in unnecessary cost. Please quantitatively explain where is this cost most likely coming from?