CateFul,
Just,what dt is saying is that just because your losing doesn't mean you've lost(you only lose when your quit outside ).Therefore,when you have not dropped,putting another position is only providing you an ordinary position nearer to current prices and so beneficial,provided it doesn't exceed your highest possible risk.
If your whole risk is 2% and your stop on your first position is 2%,then you've got no business buying/selling in again.
You must split your position up in order to operate this way.
I do so quite frequently and it works...