That's only true if all of the N contacts are infected. If I walk past 60 people on the street, there's a much lower chance than if I have lunch for an hour wit

That's only true if all of the N contacts are infected. If I walk past 60 people on the street, there's a much lower chance than if I have lunch for an hour with someone who's infected. You don't instantly get sick just by getting close to someone who is, but every second you're near them is a roll of the dice on it transmitting.