Layers of redundancy are the central risk management property of natural systems.
Redundancy allows you to survive under adversity, thanks to availability of spare parts. Look at the human body. We have two eyes, two lungs, two kidneys, even two brains (with the possible exception of corporate executives)—and each has more capacity than needed in ordinary circumstances. So redundancy equals insurance, and the apparent inefficiencies are associated with the costs of maintaining these spare parts and the energy needed to keep them around in spite of their idleness.
Nicholas Taleb wrote the above in reference to the redundancy and resiliency of natural systems. For those that still wonder about the reasons for a two way hockey played with either handedness, here is a reasoning for it.