At the activation height, all miners will ask themselves whether they should follow the rules of the soft fork, or stay with the bitcoin consensus rules Then they'll realise that they should follow the soft fork, because their block will then be valid on *both* chains So basically, just after the activation height, and just before there really is a split, miners have an incentive to apply the soft fork rules To counter this, people could create a large number of high-fee transactions with large OP_RETURNs, to encourage miners to reject the fork from the very start