For the sake of an example, allow me to assume (a) there are 10 people in your class, (b) each of you has an average of one other "risky outing" (shop at a stor

For the sake of an example, allow me to assume (a) there are 10 people in your class, (b) each of you has an average of one other "risky outing" (shop at a store, one meeting with coworkers, visit another household) a day, and (c) each outing has a 0.5% risk of transmission assuming the boxer's infected. If anyone in your group gets infected, there's a good chance you'll all catch it (you seem to acknowledge this). In that case, in one day of infectiousness, there's a 0.995^10 = 95.111% chance nobody else gets infected. So a 4.889% chance of infecting. That's low. But if you all remain infectious for 14 days, there's now only a (0.995^10)^14 = 49.571% chance nobody new is infected. So the odds are your group spread it to at least one other person. And this process will probably repeat through those new infections. Obviously, these numbers are arbitrary. It's a terrible model for an infectious disease. My point is to show how probability is very hard to reason about. It's unrealistic to expect average citizens to do this.