It does not at all defy common sense. For example if you gave me a shield that deflected 80% of bullets, it would not defy common sense to feel that shield was not effective at protecting me from someone with a machine gun.

The infectious dose of SARS-CoV-2 is as low as 10 viral particles and a single cough can release 123,000 viral particles.

If I shot 123,000 bullets at you, would you be happy with a shield that protected you from 80% of them?

At any rate, masks have proven to be incredibly effective, but the truth is that we don't know exactly how... common sense has not been particularly informative in understanding the spread of this virus.

You don’t see 100% infection rates when a positive person is in a a room. Reducing the amount of particles inhaled in such circumstances must be of use.

You would on the other hand expect a 100% fatality rate if you fired 123,000 bullets at each person in a room. So your analogy is faulty.

I hear this all the time "masks have proven to be incredibly effective" Have they? Data didn't really bear that. And there are tons of studies that day, for the lay person, we don't know. Or they say n95 and surgical masks may be effective but cloth masks are an unknown.

One of the challenges is communicating context.

20% to 80% of filters is not good enough in a healthcare setting since a provider may be in a room absolutely filled with virus particles.

In a public setting, 20% to 80% might be enough to limit incidental viral loads enough to prevent infection.

It's hard to define the effectiveness across a wide variety of settings a cloth mask might be used in.

From a mechanical perspective it would seem it would be more effective at filtering air going in rather than air going out: when you inhale it creates a lower pressure which causes a better seal around the mouth. When you exhale you create pressure under the mask which can “break” the seal and allow more unfiltered air through.

It was kind of a way to make people with valves n-95 masks feel “guilty” for wearing them.

Even good medical masks didn’t protect Li Wenliang. There was always agreement about well fitted n95 but we’re told, even by your linked article not to use those. Sorry but this seems like politics not science. Obviously if you layer enough masks you can almost get to n95 levels of protection but why not just use an n95 at that point?

The point is not that it gives you perfect protection or even n95 protection. It does give you more protection than maskless. Also the lower the viral load you're exposed to, the longer your body has to prepare. How the disease progresses is dosage dependant.

A low enough load is like a natural vaccination. You don't get sick, but you get some immunity. A high enough load and you can get the sickness very severely. It's a gradient, and masks help put you lower on that gradient than otherwise.

Sure but it’s all about quantifying that accurately so that it can be compared to for example better building ventilation. If, hypothetically, better ventilation had 100x the effect of mask wearing, then focusing attention on masks would be counter productive no? Make no mistake I’m pro mask but mostly for psychological, ethical and economic reasons. I feel their benefits in terms of personal protection are vastly overstated, often in bad faith by those with a desire to impact other people’s behavior albeit with the best of intentions.

Why can't you do both? Mask wearing is simple, cheap, and available to all. That's like asking if it's better to focus on masks or vaccines. The answer is both.

As long as it's even marginally effective (and evidence suggests it's more than marginally effective) then it is a good idea.