Probably, all the things in this world are based on a difference. Two exactly the same cars turn out to be different in further usage – one of them brakes down faster for some reasons. The same ball at hand does not make two basketball players equally skilled. And so is with Forex trading.
From my own experience, I would say that there is no perfectly profitable system, which would suit two traders at once. As a rule, one of them “drowns” (gets losses) and another “stays afloat” (earns profits). And they both were using the same system.
The major reason for this frustrating disparity is that most of the best and profitable trading systems do not have adamantly set rules. When certain market conditions are met, we often clear entry/exit points and get clear instructions to take a trade. However, it’s often left to us, the traders, to only trade the very best set-ups, so we should be capable of reading the markets and using our intuition.