Sure, nice guys can win — if they're nice guys with a lot of talent. Nice guys with a little talent finish fourth, and nice guys with no talent finish last.
Source, in full
In Koufax (1966), p. 133; as quoted in "Koufax writes: 'Sure nice guys can win'" by Ed Rumill, The Christian Science Monitor (August 29, 1966) and Total Baseball : The Official Encyclopedia of Major League Baseball (2001) by John Thorn, p. 2468