Make joining costly like a river in flood: the network charges an identity-creation fee that rises with the registration rate. One honest joiner pays a trickle, but a sybil operator registering thousands pushes the fee to its zenith, since every fake account bids the price up for the next. Like a falcon striking from above, the fee market punishes scale itself: the attacker's 10,001st identity costs far more than the first, so the marginal cost of each new puppet exceeds its expected reward and the scale economy of the attack collapses.