On Focus.

When you let your attention slide for a bit, don’t think you will get back a grip on it whenever you wish—instead, bear in mind that because of today’s mistake everything that follows will be necessarily worse. . . .

Is it possible to be free from error? Not by any means, but it is possible to be a person always stretching to avoid error. For we must be content to at least escape a few mistakes by never letting our attention slide.”

—EPICTETUS, DISCOURSES, 4.12.1; 19