Yes, but some people are infected and don't know it yet. And some people have symptoms but don't think it's worth wearing a mask, maybe because of the social stigma of wearing one in western countries. I think if everyone was wearing a mask, that would solve both problems. (of course, we know that many countries don't have enough masks).

I was saying the same thing as you two weeks ago (even in HN comments). Now I'm confined and can't leave my home without risking a fine. There may not be sufficient scientific evidence yet, but I'm starting to believe that we wouldn't be in this situation if everybody started to wear a mask in public places at the very start of the epidemics.