demo account is mainly a learning place. in here a trader basically learns how to do trade and how to do it successfully. in here a trader can trade without any fear or tension because in here all the investment is virtual. in here if a trader face big loss, then he doesn't feel any trouble. but in real trading, most of the trader feel fear form facing loss. for this they are not able to show all of their skills and that is why they really face loss or became unsuccessful. i think it is one of the reason why it happens.