Have you ever had an operation? I have had several, and each time the doctor and everyone else in the room wore a mask. Why is that you might ask, well its so they do not contaminate you with their germs while they have you opened up. You see now how and why mask help stop the spread? It prevents your germs from getting in the air. It also helps to some extent from you breathing in germs.Sure.
If an appropriate mask that's actually capable of filtering, let alone filtering well. If appropriately worn. If recognized for not being the overarching panacea some take it for.
Was simply speaking to the "science" of the reality of typical air that gets around most of today's "masks" used by the average peon. Not to the general efficacy of what "masking-up" can potentially be as a general partial step in a range of steps. (Again, it's the blind obedience to the concept that often falls down, when it refuses to consider the little wrinkles in reality that most people are facing in practice, with the gear they're using.) Two completely different situations, really.