Meditations 3.12

If thou workest at that which is before thee, following right reason seriously, vigorously, calmly, without allowing anything else to distract thee, but keeping thy divine part pure, as if thou shouldst be bound to give it back immediately; if thou holdest to this, expecting nothing, fearing nothing, but satisfied with thy present activity according to nature, and with heroic truth in every word and sound which thou utterest, thou wilt live happy. And there is no man who is able to prevent this.

Marcus Aurelius, Meditations 3.12, translated by George Long

If in obedience to right reason thou doest the thing that thy hand findeth to do earnestly, manfully, graciously, and in no sense as a by-work, and keepest that divine 'genius' of thine in its virgin state, just as if even now thou wert called upon to restore it to the Giver—if thou grapple this to thee, looking for nothing, shrinking from nothing, but content with a present sphere of activity such as Nature allows, and with old-world truth in every word and utterance of thy tongue, thou shalt be happy in thy life. And there is no one that is able to prevent this.

Marcus Aurelius, Meditations 3.12, translated by C. R. Haines