One can be wrong more than half the time and still make money.
Example: set stops at 20% up, and 10% down.
If you're wrong 60% of the time:
Wins: 40% x 20% profit = 800 (unit is "%%")
Losses: 60% x 10% loss = 600 (same unit)
Thus, being wrong 60% of the time can still be profitable.