Train the hand you think is useless.

The source

"Train the hand you think is useless." Marcus Aurelius said it in Meditations 12.6. Translated by George Long, 1862.

"Practise thyself even in the things which thou despairest of accomplishing. For even the left hand ... holds the bridle more vigorously than the right"

George Long, 1862, Meditations 12.6.

Who said it

Marcus Aurelius (121–180 AD). Roman emperor who wrote private notes to himself on a military campaign. We know them as the Meditations.

Questions

Who said "Train the hand you think is useless."?

Marcus Aurelius (121–180 AD). Source: Meditations 12.6.

What is the original wording?

Practise thyself even in the things which thou despairest of accomplishing. For even the left hand ... holds the bridle more vigorously than the right (George Long, 1862). Translated by George Long, 1862.