Let a horse drink what he will, but no when he will.
Let alane maks mony a loon.
"Let a' trades live," quo' the wife when she burnt her besom.
Let aye the bell'd wether break the snaw.
A "bell'd wether" is a ram with a bell round its neck; and the proverb means that a difficult or dangerous undertaking should be led by a person of experience.
Let folk bode weel, and do their best.
Let him cool in the skin he het in.
Let him drink as he has brewen.
Let by-ganes be by-ganes.
"'Hout, ay,' said Elliot, 'just let by-ganes be by-ganes, and a' friends again; deil ane I bear malice at but Westburnflat, and I hae gi'en him baith a het skin and a cauld ane.'"—The Black Dwarf.