[nwallin]

They don't have to have an enormous effect on an individual to have a disproportionate effect on a population. If a virus has a reproduction number of 4, and a mask prevents 1/4 infections, ten generations of the virus will infect one million people in a non mask wearing population and 59,000 people in a mask wearing population. If we assume a 1% fatality rate that's 10,000 that aren't dead.

Moreover, it's significantly fewer people who are all sick at the same time. This means more available hospital beds. It means more time to develop better treatments. Less pressure on supply chains. Less societal impact from people who can't work.

It's at best marginally effective at reducing a person's probability of catching or spreading a disease. But in the face of potentially exponential growth, reducing that base by a few percentage points is a huge win.

That's why vaccines are incredibly effective despite being only 90% effective. Disease simply doesn't spread when 90% of the population is immune, no matter how virulent the disease is.