Boiling it down
The easy 1, 2, 3 of stoicism may be presented as:
If you can change it, it doesn’t deserve your worry. Go ahead and make the change. Just do it!
If you can’t change it, it doesn’t deserve your worry. You can’t fix it, so why stress?2
If you worry about it anyway, you are simply inviting it to tyrannise and traumatise you, indefinitely. Rumination is the worst.