A mask only works if the wearer knows how to use a mask.
For varying values of 'work'. If you wear a mask incorrectly, does it do anything at all? I would suggest it has
some effect - it won't be the 'proper' working fully protective effect, but it would surely be better than nothing at all, wouldn't it?
Kind of like if you wear a crash helmet incorrectly it's not going to be as effective as if you did it up properly, but there's a non-zero possibility that it will lessen a bash on your bonce all the same. [OK, not quite analogous because an incorrectly worn helmet might kill you whereas a mask won't, but let's not go down that kind of rabbit hole.]