How often do we read something that gets filed in the memory in the form of a paraphrase?
Many educated people, civil war generals and others habitually and continually have read their Marcus Aurelius. In the Meditations, they encounter quotes like this:
Now much time and leisure doth he gain, who is not curious to know what his neighbor hath said, or hath done, or hath attempted, but only what he doth himself, that it may be just and holy? or to express it in Agathos' words, Not to look about upon the evil conditions of others, but to run on straight in the line, without any loose and extravagant agitation. (Marcus Aurelius, Meditations, Number XV)(No I don't know who Agathos is.) A number of editions of the Meditations are still in print. The classical stoic may be an accessible handle on life for people in business and politics. I would rather have them all reading old Marcus than old Marx, to tell you the truth.
To return to our quote about the thief of joy. What is more precious than time? What is more pernicious than someone or something that robs us of valuable time? While Marcus Aurelius made the comment positive with respect to time and negative about comparing or curiosity, the succinct aphorism attributed without documentary citation of attribution turns it into a positive about curiosity (comparison) and negative (a thief) about joy/time/value.
Viva Marcus (Aurelius) and Mark (Twain)! Oh, and down with Marx.