Every trader needs to master their psychology to be able to profit from the market. Otherwise, they will be messed up by the market once they get hit by loss and they will lose confidence of the little they even know. Nothing messes a trader up like loss of confidence in their trading strategy or plan. Risk Management/Money Management is benched on trading psychology. It's an important aspect of trading.
It is almost the most important aspect of trading because even when you master the other sides of trading but have not yet mastered the psychological side, chances of making wrong decisions will still be very high. The psychological aspect of trading can affect your decision to either enter a trade, exit a trade or take profit too quickly before you can get maximum or get out of the market with a loss as a reaction due to fear, as soon as your predictions show a sign of pullback. Good traders are psychologically sound.