If you are distressed by anything external, the pain is not due to the thing itself, but to your estimate of it.
After a close friend betrayed him in court politics, Marcus did not lash out. He reminded himself that the sting he felt was not from the act, but from his judgment of the act. It was his mind assigning value — and pain. By choosing a different interpretation, he remained composed.
Events are neutral — it is your interpretation that gives them meaning.
"There is nothing either good or bad, but thinking makes it so."