Charles H. Spurgeon on Psalms 137:5

Let my right hand forget her cunning. There is a striking and appropriate point in this, which has been overlooked. It is, that, as it is customary for people in the East to swear by their professions, so one who has no profession —who is poor and destitute, and has nothing of recognized value in the world —swears by his right hand, which is his sole stake in society, and by the "cunning" of which he earns his daily bread. Hence the common Arabic proverb (given by Burckhardt) reflecting on the change of demeanour produced by improved circumstances: —"He was wont to swear `by the cutting off of his right hand!' He now swears `by the giving of money to the poor.'"The words, "her cunning", are supplied by the translators, in whose time cunning (from the Saxon "cannan", Dutch konnen, "to know") meant "skill"; and a cunning man was what we should now call a skilful man. In the present case the skill indicated is doubtless that of playing on the harp, in which particular sense it occurs so late as Prior:

"When Pedro does the lute command,

She guides the cunning artist's hand."

Modern translators substitute "skill"; but perhaps a term still more general would be better —such as, "May my right hand lose its power." —John Kitto, in "The Pictorial Bible."