"Mastering your emotions" if you mean, controlling your emotions, is not balanced or healthy. Mastering your emotions means listening to them as a critical feedback to your environment and then rationally controlling your response.

Rational thought is complimentary to emotional thought. Rational thought is slow, reflexive, and highly focused. Emotional thought is affective; it is your mind telling you how something is affecting you.

E.g. Anger tells you some boundary has been violated. It's the rational part that allows you to analyze that feeling and respond appropriately (telling someone to back off or getting a snack because your blood sugars are low)