That's a well known fact about how masks work in general, yes. They have a large effect on transmission from the wearer and a comparatively small effect in pre

That's a well known fact about how masks work in general, yes. They have a large effect on transmission from the wearer and a comparatively small effect in preventing transmission to the wearer. However, when you have a limited supply of masks, it's impossible to give them out to every potentially-infected person, so saving them for high-risk people (like healthcare professionals, who also have the highest risk of becoming infected themselves) is still rational.