It only takes contact with one infected person
Of course, it’s just that one time you weren’t careful that could change everything. You only have to interact with one infected person to get it. You don’t get it by interacting with 100 infected people. All you have to do is get too close to one infected person, and it could be that one time out of 100 you didn’t wear a mask, and it’s like all those 99 other times were for nothing.