Enchiridion 5

It is not the things themselves that disturb men, but their judgements about these things. For example, death is nothing dreadful, or else Socrates too would have thought so, but the judgement that death is dreadful, this is the dreadful thing. When, therefore, we are hindered, or disturbed, or grieved, let us never blame anyone but ourselves, that means, our own judgements. It is the part of an uneducated person to blame others where he himself fares ill; to blame himself is the part of one whose education has begun; to blame neither another nor his own self is the part of one whose education is already complete.

Epictetus, Enchiridion 5, translated by W. A. Oldfather

Men are disturbed not by the things which happen, but by the opinions about the things: for example, death is nothing terrible, for if it were, it would have seemed so to Socrates; for the opinion about death, that it is terrible, is the terrible thing. When then we are impeded or disturbed or grieved, let us never blame others, but ourselves, that is, our opinions. It is the act of an ill-instructed man to blame others for his own bad condition; it is the act of one who has begun to be instructed, to lay the blame on himself; and of one whose instruction is completed, neither to blame another, nor himself.

Epictetus, Enchiridion 5, translated by George Long

What disturbs men's minds is not events but their judgements on events. For instance, death is nothing dreadful, or else Socrates would have thought it so. No, the only dreadful thing about it is men's judgement that it is dreadful. And so when we are hindered, or disturbed, or distressed, let us never lay the blame on others, but on ourselves, that is on our own judgements. To accuse others for one's own misfortunes is a sign of want of education; to accuse oneself shows that one's education has begun; to accuse neither oneself nor others shows that one's education is complete.

Epictetus, Enchiridion 5, translated by P. E. Matheson