In 1892, Dmitri Ivanovsky discovered that viruses are filterable, which means they can pass through filters. The 1918 Spanish flu pandemic showed that people wearing masks didn't slow the spread of the virus.
In 2009, we saw medical experts on the news discussing how the trend in Asia to wear masks was totally ineffective against the H1N1 virus. Now when the SARS-CoV-2 started spreading through China, once again many medical experts said the masks were useless. One early story stated that first responders and other medical staff using the N95 masks were catching COVID-19.
Then suddenly everything changed. There was a rally by the American people to make and sew masks to protect health-care workers. Suddenly places were requiring people to wear masks and some people are being arrested for not wearing them. Mainstream media is attacking the president, vice president the COVID-19 response team, governors and others for not wearing masks. In response officials said masks create a false sense of security and it is better to maintain social distancing and proper hygiene.
A group of doctors in South Korea did a study because the doctors saw a shortage of N95 masks for health care works and wanted to find an effective alternative. So they tested cotton masks and the surgical (paper) masks. The conclusion was that they were ineffective in preventing the spread of the virus. The virus went straight through. They are still testing to find effective alternatives.
Even if the masks were effective so many people today don't wear them properly. I've seen many store employees and fast food workers wear them like beards, (not covering nose and mouth) on their heads as if they had blow holes, around their neck or covering only the mouth.
Masks also need to be changed frequently, in hospitals they are supposed to be changed after each patient and also if they build up moisture. The moisture makes them less effective. After you take a mask off it needs to be discarded, or immediately cleaned and disinfected before reuse. Frequent touching of the mask also increases the chance of spreading the virus. If you choose to wear one, great, but do it properly. If choose not to, you should be fine with social distancing, it's been working very well so far.