From a Persian poem of a few hundred years ago:
انچه خواهد شدنا
انچه نخواهد شدنا
Literal word by word to reflect grammar:
Whatever will be(come)
Whatever won’t be(come)
What will be, will be
What won’t be, won’t be
Why should you worry when what will happen, it will, regardless of your worries….And what use are worries for event that won’t happen?
In effect stating the futility of worry and the importance of recognizing the Determined state of Destiny, while indirectly encouraging effort (instead of worry).