Full Idea
Since he has harmed himself by wronging me, shall not I harm myself by harming him?
Gist of Idea
If someone harms themselves in harming me, then I harm myself by returning the harm
Source
Epictetus (The Discourses [c.56], 2.10.26)
Book Reference
Epictetus: 'The Discourses, The Handbook, Fragments', ed/tr. Gill,C [Everyman 1995], p.97
A Reaction
I am very keen on this idea. See Hamlet's remarks to Polonius about 'honour and dignity'. The best strategy for achieving moral excellence is to focus on our own characters, rather than how to act, and to respond to others.