E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Last. (Anglo-Saxon lást, a footstep, a shoemakers last.)
The cobbler should stick to his last (Ne sutor ultra crepidam). Apelles having executed a famous painting, exposed it to public view, when a cobbler found fault because the painter had made too few latchets to the goloshes. Apelles amended the fault, and set out his picture again. Next day the cobbler complained of the legs, when Apelles retorted, Keep to the shop, friend, but do not attempt to criticise what you do not understand. (See WIGS.)