Summary:
Epictetus defines invincibility as the ability to remain unaffected by anything beyond one’s reasoned choice. True strength lies in maintaining inner peace and not allowing external events or circumstances to disturb one’s emotional and mental balance.

Interpretation:
For readers of The Daily Stoic, this quote highlights the Stoic practice of focusing only on what is within your control—your thoughts, actions, and choices. In real life, this might mean facing criticism or failure without being shaken because these events are external and beyond your influence. For example, if you lose a job, instead of despairing, you could focus on how to respond constructively, such as seeking new opportunities or improving your skills. By aligning your actions with reason and virtue, you cultivate an unshakeable inner strength that no external challenge can defeat.