1What's going on in everyone's head
Two simple things make a crowd
You only need two ideas. Watch each one:
Everyone has a secret number
"I'll only come if at least THIS many others are coming." Some friends are easygoing (a low number — they'll come to a quiet party). Some are shy (a high number — they only show up once it's already busy).
Everyone watches everyone
Nobody decides alone. If a few people leave, the room gets emptier — which can push the next person past their own number. So each choice quietly pushes on the next choice.
2Two kinds of crowd
The plodders vs the copycats
A crowd can be put together two opposite ways:
The plodders
Everyone's number is zero. They come whether it's packed or empty. Nobody is watching anybody.
The copycats
Everyone has a real number, so each person is checking the headcount before they decide.
3Your turn — set the mood
Make the copycat crowd pickier and watch the room
Here's a copycat crowd. Drag the slider to make everyone pickier — needing more friends before they'll come. The room settles to a steady headcount. Hunt for the spot where it suddenly empties out.
4Now balance it on the edge
Can five steady guests stop a chain reaction?
A fresh party has 30 guests. Five will stay even if nobody else does. The other 25 have crowd rules: they need 6, 7, 8… up to 29 other guests. One of the guests who needs 29 stays home. Predict how far the leaving will spread.
Guess before you remove anyone
Everyone starts at the party. After that one guest stays home, each remaining guest checks how many OTHERS are still there. When nobody else wants to leave, how many will remain?