In the case of the 2003 blackout the error on the grid took the form of overgrown trees and the error on the computers took the form of a line of code that disallowed simultaneous incoming data reports. Each error had small but significant effects on the actual physical infrastructure they came into contact with, while the way in which this physical infrastructure was designed—its logic—allowed for stochastic propagation of negative effects. Which is to say: the cascade and then the blackout.
