I would guess the big difference is the timing and non-passive nature of the stickers. Let's say I go to work and see that everyone has a sticker, I've already

I would guess the big difference is the timing and non-passive nature of the stickers. Let's say I go to work and see that everyone has a sticker, I've already lost the social value of voting because if I vote after work, no one sees it. Also, I have to actually see the people who vote. In this method, he tells you ahead of time that I'm going to be left out, so I can still gain some social utility for voting.