Nothing is more wretched than a man who traverses everything around, and pries into the things beneath the earth, as the poet says, and seeks by conjecture what is in the minds of his neighbours, without perceiving that it is sufficient to attend to the daemon within him, and to reverence it sincerely. And reverence of the daemon consists in keeping it pure from passion and thoughtlessness, and dissatisfaction with what comes from gods and men.
Among other things, which to consider, and look into thou must use to withdraw thyself, let those two be among the most obvious and at hand. One, that the things or objects themselves reach not unto the soul, but stand without still and quiet, and that it is from the opinion only which is within, that all the tumult and all the trouble doth proceed. The next, that all these things, which now thou seest, shall within a very little while be changed, and be no more: and ever call to mind, how many changes and alterations in the world thou thyself hast already been an eyewitness of in thy time. This world is mere change, and this life, opinion.
Marcus Aurelius – Meditations