Differences Between Demo Trading and Real Trading
by Boris Schlossberg
Always remember, however, that demo trading is in no way similar to trading real money. You may be perfectly calm about sustaining a $10-million loss with fake money, but might become completely unhinged over a $100 loss in your real account. To make demo trading as productive as possible, you need to trade the demo account as though the money were real. For example, if you plan on funding your real account with $5,000, don't trade a demo account that has $100,000. The thrill of a $1-million trade can give you a temporary high, but it will only hurt when you have to transition to a real account, because you will have no sense of proportion and will likely make drastic errors in judgment.
Source: http://www.investopedia.com/articles/forex/05/DemoTrade.asp