The thing to keep in mind is that blocking 50% of the particles does not mean a 50% reduction in infection. It may mean a 50% reduction in infection -- or it may mean a basically zero percent reduction. It depends on the exposure.

Say that in a particular covid-filled room you have a 50% chance of being infected after 5 minutes and a 99.9% chance of being infected after an hour. Under a simple model, if you wear a mask that blocks half the particles, your chance of getting coronavirus in 5 minutes would be reduced to 25%, but your chance of getting it after an hour would be 97%. So if cloth mask is your primary defense against covid, you are eventually going to get covid if you are trying to live anything close to a normal life. Blocking 50% of particles is like wearing an condom that only blocks 50% of the sperm or an umbrella that blocks only 50% of the rain.