[evgeniysharapov]

One can look at it as what's the null hypothesis. Presumably it should be "masks DO NOT work". But for whatever reason, media, tech, politicians, doctors chose opposite as a null hypothesis - "Masks DO work" shifting the burden of proof. Neither has been proven though. There were studies, e.g. DENMARK-19, etc. but after this became a political and ideological issue it seems no one interested to find the truth to the question "do masks work in reducing transmission of respiratory viruses". Notice that there's also question - what does it mean "work", let's say it reduces number of viral particles but that reduction has little effect on transmission, it should mean it doesn't work.