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.

Than you are describing human fallacy.

Even when you only think you are infected or there is a good chance => wear a mask

I strongly disagree.

1. Heaps of people have the virus without showing symptoms

2. No-one wants to be treated like a leper, so everyone needs to wear masks. If only the sick wear them, then self-deception and avoiding social opprobrium will cause people to avoid wearing masks, and the selfish will not wear masks

3. If home-made masks help even 20%, that would make a massive difference to infection rates over time due to exponential growth (think compounding interest).

4. Everyone in smart Asian countries wears them for a reason.

5. There is a reasonable chance that the reason Japan has low infection rates is due to masks. Everyone should be jumping on whatever actions that have a percentage chance of working (so long as they don’t carry significant risk).

Other example is Taiwan. Everybody wears a mask there since the first cases. We don't know for sure it's the reason why they have so few cases but there are good reasons to believe so. I had friends there and thought I was smart telling them it was useless to wear a mask without symptoms (which was actually WHO recommendations)... Maybe WHO recommendations took into account the fact that masks weren't in sufficient quantities. For this strategy to work, you need enough mask for everybody, otherwise people would start hoarding masks. Maybe this will be the strategy post-confinement.

Taiwan were preprepared for an outbreak, and started acting on the 31st December: https://jamanetwork.com/journals/jama/fullarticle/2762689

They are using many overlapping layers of solutions to contain the virus.

Everyone using masks is surely a great help in reducing the R0, but it is the breadth of multiple solutions that is protecting Taiwan so far.