Was going to suggest this too.

Stoicism is a state of mind. A perception of your reality.

A way to not let externalities bother you and shake your way of being.

For example. I said lets go dutch to a group of friends while eating out.

One member at the table got offended because 'I insulted a group of people'

That person is not at inner peace if a word offends them enough to show distress.