Because of the nature of our interconnectivity in a complex network, if one of us fails all of us fails. The example of a power network breaking down causing multiple power outage in several state is a perfect example. "When a network acts as a transportation system, a local failure shifts loads or responsibilities to other nodes." (Barabasi, 2001) This will cause the whole system to fail because the neighbors cannot afford the load. It's like a chain-effect that won't stop. Cascading failure is the price to pay for topological robustness. If the hub is attacked, all the links linked to the hub will fail.
This reminds me of what we learned in physics about electronic current circuit. I do not remember the exact terminology and the theory behind it but I do see the connection.
Circuits are designed in a way that if one fails there will always be another one that works. It might not be self-explanatory in the diagram; however, if we think about christmas light we can understand cascading failure. Some older version of christmas lights do not have the circuit designed to be cascading failure proof; therefore, if one light bulb burns out, the ones following it burn out too. This issue can be prevented if the circuit is designed differently so that each light (node) is an individual. (At this case, it would lower the interconnectivity. But it's not like christmas lights need that much interconnectivity anyway.)
All networks, ranging from the internet to the tangled economic web, survived, a vivid demonstration of the fundamental differences between the vulnerability of centralized human planning and the resilience of self-organized network design.
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