Much as a bar's cover charge is a filter. Conversation I had a few years back, at New Years:

"Why would anyone pay $100 just to enter a bar?"

"To be at a bar with people who can afford to pay $100 to enter."

A similar role, though different mechanism, is described by Joseph Wood Krutch: "There's nothing like a good bad dirt road to screen out the faintly interested and to invite in the genuinely interested." Often recast as "bad roads make good filters".

https://www.greensboro.com/the-highway-less-traveled/article...