How can the demo account for backtesting be different from the current account?

Gouxiang Lan  
How can the demo account for backtesting be different from the current account? And it's very different, can anyone tell me why?
Hung Wen Lin  
The one is real world and other one is dream world.
Tiecheng Fu  
Gouxiang Lan:
How can the demo account for backtesting be different from the current account? And it's very different, can anyone tell me why?

demo trade

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