The purpose of a good system is to replace luck by a systematic approach. Luck should be banned to the max out of your system. System is the opposite of luck in trading. System means know what you do and why. Luck is have no clue but make money by accident. Till one day a real accident happens and you run out of your luck too (wiped out).
Would you care to put a gun to your head betting on outcome of any single trade? I wouldn't.