Whether you can make money in the long run depends on two things: your probability of winning and the size of each win or loss.

The combination of these two is the true core of trading—the expected value.

Calculating expected value is simple:

“Win rate × Profit per win” minus “Loss rate × Loss per loss.”

Looking only at win rate is incomplete, because the amount won or lost is the real key to profit and loss.

So a high win rate alone is meaningless.

Even if you win nine times and lose once, as long as that one loss is big enough, all your small wins before can be wiped out in a single instance.