Green’s Dictionary of Slang

any situation in which luck, not judgement, is of paramount importance.

1964		in Wash. Post 2 Aug. G3/3: But we made it plain that the whole project was a crap shoot, and they should invest only what they could afford.
1978		Chicago Trib. 23 Mar. C11/1: The latter deal led one Tribune source to observe: ‘It was a crap shoot from the time the agency was purchased and they [i.e. the new management] couldn’t get lucky.’.
1987		T. Wolfe Bonfire of the Vanities 59: In no time, markets of all sorts became heaving crapshoots.
1997		C. Hiaasen Lucky You 103: Investing in real estate was a crapshoot, as everybody knew. Sometimes you won, sometimes you lost.
2001		(con. 1964–8) J. Ellroy Cold Six Thousand 429: Sammy shrugs — life’s a crapshoot, baby.
2018		M. Mesko Confessions of a Caddie 88: Every day’s a crapshoot when you caddie at LA Country Club.