They are Actively / Purposely / Consciously trying to not worry about things that are beyond their control.
Then, I would think, they are making it about themselves, not about how God is able.
And possibly they are mainly concerned with how they are feeling, not about relating with others and feeling for others.
I can trust God so I am in peace, and then feel for others, caring about them . . . not only about how they feel and have control of their own minds, but caring about how God is able to change their character into the image of Jesus so they are pleasing God while intimately enjoying Him and doling His will. It seems, though, that the stoicism you are representing is mainly about living in a person's own mind trying to control what is going on there. That can be isolating from God and from how God has us loving others as family in Jesus and also caring for enemies in Satan's kingdom.
Have you read any stoic statement or claim about loving others, and how to become in our character? . . . not only calm about surrounding things, but how a person is becoming. They are limited to how their character is!! Their character has so much to do with how they are capable of disciplining themselves; and our human character without God is helpless > "without Me you can do nothing," Jesus says in John 5:15.
But, also, there are Christians who preach, it seems, how much their "free will" . . . which is human . . . is capable of doing. And they can be "trying" to discipline their own selves. And their human trying fails.
But I find that Biblical Christianity is God's grace first bringing a person to Jesus, and to trusting in Jesus. This trusting is very personal and intimate, bringing us into ongoing personal sharing with God while God in us changes us so we are submissive to Him in His peace. Our character becomes submissive so we are sharing with Him in His own love (Romans 5:5) while doing what He has us doing with Him. And we discover how He has us loving as family with other children of God, and we care for any evil people, at all . . . like Jesus on the cross.
So, this is very personal, with God Himself. It is not a theory or philosophy, then.
But this is what God is doing . . . while we *discover*, each moment, what He does with us. So, we are not guided by some idea that we try to get ourselves to live by, but God guides us by means of actually working in us to do what He means by His word >
"for it is God who works in you both to will and to do for His good pleasure." (Philippians 2:13)
And I now think of this > in case I really am with God, like this, God has people praying for me to be so blessed with Him in His love. God includes us, uses us, to help each other to live the way the Bible really means. So, I need to pray this to others, since I am included in ministering this.