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you may be a winner with demo money but end up losing money when playing for real
putting it simple: it's usually better to go with real money from start, even if it's a little amount.
It is not necessarily so, but it's possible, so overall I agree with you about betting with little amounts from the start instead of betting with fake money.
It's just that there's a myth among gamblers, it concerns slots mostly, that you are winning playing in demo mode, but once you switch to real money, you start losing. And I want to emphasize that that's just a myth without any evidence whatsoever.