Study, not in order to add anything to your knowledge, but to make your knowledge better. - Epictetus

Men are disturbed, not by things, but by the principles and notions which they form concerning things. (5). (Enchiridion 5)

Verlange nicht, dass das, was geschieht, so geschieht, wie du es wünschst, sondern wünsche, dass es so geschieht, wie es geschieht, und dein Leben wird heiter dahinströmen

First to those universal principles I have spoken of: these you must keep at command, and without them neither sleep nor rise, drink nor eat nor deal with men: the principle that no one can control another's will, and that the will alone is the sphere of good and evil.