Your math assumes you are the only person using masks and have daily exposure. It breaks down when people are in isolation, which many of us now are. You are n

Your math assumes you are the only person using masks and have daily exposure. It breaks down when people are in isolation, which many of us now are. You are not out daily, so a 50% reduction is a 50% reduction, and with luck you never accumulate enough to get sick. If everyone wore masks, then every ones daily exposure would drop dramatically. You get 50% less intake, and infected people are emitting much less too. You have pretty much eliminated air born transmission, and can now focus on hands and eyes.