A calm mind = a strong mind

The nearer a man ​comes to a calm mind, the closer he is to strength.
The nearer a man comes to a calm mind, the closer he is to strength.” – Marcus Aurelius

If someone knows how to push your buttons, to get you worked up and out of sorts just by something little that they say or do, they can easily manipulate you. The less reactive you can be, the more power you can have. If you take a moment to pause, you can choose your response – to let things go, to address them calmly and respectfully, or to be stern and forceful. But the key here is you are making the decision on how to respond. That is strength. Reaction to an event is not.