From Musonius Rufus on How to Live by Ben White:
"Of everything that exists, God has put some in our control, some not. He has put the noblest and most excellent thing in our control (the reason He himself is happy), that is, the power of using our impressions.
When correctly used, it means serenity, cheerfulness, constancy - justice and law and self-control - virtue overall. All other things He has not put in our control. Thus we ought to emulate the mind of God - dividing up things like this - we ought to completely claim the things in our control - entrust what isn't to the universe: gladly give it whatever it asks for - our children, our country, our body, anything."
~ Gaius Musonius Rufus