To rephrase what I took to be the essential gist: if you go from meeting 0 people to meeting 1 person, you are only exposing yourself to (some) additional risk. But if you are regularly seeing 99 people, then by adding on a hundredth person, you are now exposing all of those 99 to potentially getting infected from the hundredth.
Thus going from 99 to 100 is worse than going from 0 to 1, since 0 → 1 exposes no people other than yourself to added risk, whereas 99 → 100 exposes 99 other people than yourself to added risk.
To rephrase what I took to be the essential gist: if you go from meeting 0 people to meeting 1 person, you are only exposing yourself to (some) additional risk. But if you are regularly seeing 99 people, then by adding on a hundredth person, you are now exposing all of those 99 to potentially getting infected from the hundredth.
Thus going from 99 to 100 is worse than going from 0 to 1, since 0 → 1 exposes no people other than yourself to added risk, whereas 99 → 100 exposes 99 other people than yourself to added risk.