Begginner is definitely correct. Psychological differences between demo and live can make a huge difference, and there is always the possibility that some brokers might deliberately manipulate entries and exits on demo accounts to increase profitability.
Even un-manipulated demo accounts also are much less likely to have
requotes and
slippage, especially at times of high
volatility.
In general, it's a good idea to initially test a new
EA or other trading method on demo. If it returns a decent profit on demo, then try it live trading VERY small amounts of cash.
Success in demo means it might work on a live account.
Failure in demo is a good indication it won't work on a live account.
If you really want to fast track something, you can skip demo trading. To do this and not get wiped out, find a broker that offers
nanolots (1 cent per pip), open a small account, and test live.