The Serenity Prayer so neatly encapsulates the lessons of Stoicism and Buddhism: Tranquility comes from focusing on what you can control, and letting go of what you cannot.
God grant me the serenity
to accept the things I cannot change;
courage to change the things I can;
and wisdom to know the difference.
When you can direct your focus to what matters, you can also be a steadying force for other lives you care about.
“Be the promontory against which the waves break.”
~Marcus Aurelius, Meditations (Book)