its not that 50% of the traders are successfull because the market provides a 50/50 change of success.
This only means that you have 50% of succes at a single 1 to 1 trade, if you plan to let it run until you loose or win.
But the problem is that you can decrease your own probability even more that you can increase it.
Let me explain it with a casino example =p
When you gonna play roulette, and you gonna put your money on black or red, that you have nearly a 50/50 change of success on a single bet. Let's say you walk in with $10 and decide to put that on red, and if you win you walk out of the casino with $20, then you have a chance of almost 50% walking out the casino dubbelde your money!..
But in reallity, most people just walking into a casino and keep playing until they blow al the money they took, including the profits they made before....
This decrease the probability of succes..
This is the same in the forex market.. When you can't hold on to a solid money management plan, you will blown out of the game before you know your in there.. And there your 50% change of winning go's...
Even if you are capable of holding on to good MM, but you are to emotional to hold on to the market rules like you planned it, and you have a negative long term outcome because of that, you will die slowly and there your changes go