Good point, Sunshine.
Also, if there was such a system can produce 50% consistently, I would like to help the system's owner - Many brokerage firms offer margin or line of credit (alike HELOC against your equity with RE; LOC against your stocks/funds in brokerage account) with interest rates in the range of 3.5% - 7%; so the system owner can get unlimited $$ by repeating "borrowing, gaining the gap; qualify to borrow more; gaining more......". Mathematically, as long as the base is greater than 0, you can go all the way to infinity after unlimted repeating....
I did admit that short term trading is possible. When I participated the games initiated by Fidelity (use fake money but real trading), I picked the most risky strategy and double my base within a month.
