More of a guideline, actually...
So in laymans terms, when the law of conservation of momentum and quantum theory fight, quantum theory wins?
Sounds a bit odd to me that we can observe macroscopic violation of CoM by running one of these engines for a while. Usually the universe applies some kind of accountant's rounding to stuff like this, so over time the effect of quantisation leads to as many round-ups and downs, and no net change is observed.
Can we get quantum theory and the second law of thermodynamics to fight next? That'd be one worth watching.