What it is
Stoicism is a Greek school of philosophy founded by Zeno of Citium around 300 BCE. Epictetus (about 55 to 135 CE) was born enslaved, studied Stoicism in Rome, and after he was freed taught there until he was banished; then he ran a school in Greece. His student Arrian recorded his lectures as the Discourses and condensed them into the Handbook.
His central split: some things are up to us, our judgments, impulses, desires and aversions, and some are not, our body, possessions, reputation and position. For Epictetus, our faculty of choice is the true self, and it can’t be taken from us. Freedom comes from putting our effort where it belongs.
How it shows up for me
It’s the oldest version of locus of control I know, and it came from a man who had every reason to feel powerless. When I’m spinning, “is this up to me?” is the fastest question I have.