The first rule of day trading is never to hold onto a position when the market closes for the day. Win or lose, sell out. Most day traders make it a rule never to hold a losing position overnight in the hope that part or all of the losses can be recouped. For one thing, brokers have higher margin requirements for overnight trades, and that means additional capital is required. There's a good reason for that. A stock can go down or up on overnight news, inflicting a bigger trading loss on the owners of shares.