You dont know for first ~5-6 days whether you are infected or not.
https://www.businessinsider.com/people-are-making-diy-face-m...
Don't worry too much about effectiveness of DIY face masks - in few months Respilon and other Czech companies will put on market face masks made from nanomaterials which filters virus much more effectively ;)
OK, I think that the mask over your own face is to prevent viral spread in largish water particles caused by coughs and sneezes, not general breathing (I'm not sure general breathing spreads much virus anyway, but I don't know).
So if you are infected and not showing symptoms ie. not coughing/sneezing then arguably the mask is not doing anything.
Arguably not, but we need more data - can anyone comment with sources?
People cough and sneeze all the time even if they're not sick.....
It prevents you from touching your mouth and your nose and thus getting it on your hands.
There is an excellent video visualising the spreading of germs:
https://www.youtube.com/watch?v=I5-dI74zxPg
How To See Germs Spread (Coronavirus) by Marc Tober
Maybe that convinces you.