  Controlling self-organizing systems is challenging because the system
responds to the controller. Here we develop a model that captures the essential
self-organizing mechanisms of Bak-Tang-Wiesenfeld (BTW) sandpiles on networks,
a self-organized critical (SOC) system. This model enables studying a simple
control scheme that determines the frequency of cascades and that shapes
systemic risk. We show that optimal strategies exist for generic cost functions
and that controlling a subcritical system may drive it to criticality. This
approach could enable controlling other self-organizing systems.
