Two identical tissues must rebuild the same pattern: Wolpert's French flag, the classic problem of how cells know where they are. Each cell only knows whether it sits near cells of its own kind. Cells that are happy refuse to move. On the right, cells also feel their neighbors' stress, so a satisfied cell next to a struggling one will step aside for it. Drag across either tissue to injure both the same way.
Stress stays inside the cell that has it.
A cell feels the strongest stress around it.
Set spreading to 0% and the right tissue jams just like the left. The rules are otherwise identical.
Shreesha and Levin propose stress sharing as one of the mechanisms that binds cells into a larger self. If my neighbor's error raises my stress, its goal has become partly mine, and the boundary of "me" grows.
Stepping aside costs a happy cell its own good position for a moment. The left tissue never pays that cost and stalls in a local optimum. The right one pays it and keeps going.
No cell holds the flag. The pattern is reached because the stress landscape tells each cell when to move, which is how Levin frames morphogenesis: navigation toward a goal, not execution of a plan.