The best example of it "flying" is the evolution of the economic systems of the industrialized world in the direction Marx laid out and away from the system he described as "capitalism" since his time, and particularly from the early-mid-20th Century. Far from a perfect example, but there it is.
Lots of people say "Marxism can't work" because Leninism, which, viewed cynically, is a thin veneer of Marxist rhetoric around naked authoritarianism or, viewed generously in its own overt terms, is an adaptation of Marxism to bypass the extensive period of the development of market capitalism and proletarian class consciousness under it, has had pretty poor results in the real world. But Leninism's failures can tell something about Leninism, but very little about Marxism.