A dictionary of Proverbs (Oxford Paperback Reference)

doing see if a THING’S worth doing, it’s worth doing well.
dollar see ANOTHER day, another dollar.
What’s DONE cannot be undone
Also found in the terser, more casual form what’s done is done. Cf. SOPHOCLES Ajax 1. 378 7. t?7 7t-njii-;: и?-/ ••?(' things could not now be otherwise; early 14th-cent.
Fr. mez quant ja est la chose fecte, ne puet pas bien estre desfecte, but when a thing is already done, it cannot be undone.

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  c 1450 King Ponthus in Publications of Modern Language Association of America (1897) XII. 107 The thynges that be doone may not be undoone. 1546 J. HEYWOOD Dialogue of Proverbs I. x. C4 Things done, can not be undoone. 1605-6 SHAKESPEARE Macbeth III. ii. 12 Things without all remedy Should be without regard. What’s done is done. Ibid. v. i. 65 What’s done cannot be undone. 1791 G. WASHINGTON Letter 1 Dec. in Writings (1939) XXXI. 433 What has been done cannot be undone, and it would be unfortunate.. if disputes amongst the friends of the federal City should Arm the enemies of it with weapons to wound it. 1818 S. FERRIER Marriage III. xxi. I hope you will think twice about it. Second thoughts are best. What’s done cannot be undone. 1967 H. HARRISON Technicolor Time Machine vii. What’s done is done.. I’ll see you don’t suffer for it. 1998 K. NEVILLE Magic Circle 92 ‘And although I am very, very sorry I involved you in this, Ariel, what has been done cannot be undone.’ ■past
  

done see also DO as you would be done by; whatever MAN has done, man may do; NOTHING should be done in haste but gripping a flea; the SOONER begun, the sooner done; if you WANT something done, ask a busy person; WELL begun is half done.
A DOOR must either be shut or open
Said of two mutually exclusive alternatives. Cf. Fr. il faut qu’une porte soit ouverte ou fermёe, it is necessary that a door be open or shut.

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