If you study Behavioral Finance, you'd very much know how the markets just work based on traders' psychology. So it's true that it's just a mental game, but a very tough mental game! There's this thing called Loss Aversion, where the degree of unhappiness you feel when losing is much greater than the degree of happiness you feel when winning. So the tendency is for people to be very irrational when they lose (multiply their risk, withdraw all their money, etc.). Keep this in mind! You need to find the right balance between not getting excited when winning and not getting stressed out when losing. Many years of experience in trading will teach you this.