It's a matter of time, distance, and saturation/tipping point of the viral load. There's a certain point where enough of the virus has escaped the infected's mouth and nose, and built up around him, that exposure is inevitable.
Spend 15 minutes within 6 feet of even a person that's wearing a cloth or surgical mask, and you are within a cloud of virus that has escaped the mask and has reached a saturation level sufficient to infect you.
The virologists have been very clear on this time/distance calculation for over two years now. The masks are irrelevant at that time/distance. It's a cloud in the air around an infected person. The evidence confirms this, especially with the most recent strain. Scores of thousands of people are being infected regardless of mask wearage. Both my son and daughter were, at school. My wife was, at work.