The Jargon File (version 4.4.7, 29 Dec 2003):

big win
 n.

    1. [common] Major success.

    2. [MIT] Serendipity. ?Yes, those two physicists discovered
    high-temperature superconductivity in a batch of ceramic that had been
    prepared incorrectly according to their experimental schedule. Small
    mistake; big win!? See win big.


The Free On-line Dictionary of Computing (30 December 2018):

big win

    An MIT term for a Good Thing or a lucky accident.

   [Jargon File]

   (1996-03-06)