The Enchiridion (18-20)

When a raven happens to croak unluckily, be not overcome by appearances, but discriminate, and say, Nothing is portended to me; but either to my paltry body, or property, or reputation, or children, or wife. But to me all portents are lucky, if I will. For whatsoever happens, it belongs to me to derive advantage therefrom.

You can be unconquerable, if you enter into no combat in which it is not in your own power to conquer. When, therefore, you see any one eminent in honors or power, or in high esteem on any other account, take heed not to be bewildered by appearances and to pronounce him happy; for if the essence of

Remember that it is not he who gives abuse or blows who affronts; but the view we take of these things as insulting. When, therefore, any one provokes you, be assured that it is your own opinion which provokes you. Try, therefore, in the first place, not to be bewildered by appearances. For if you once gain time and respite, you will more easily command yourself.