In many complex systems, efficiency, redundancy, and resiliency pull in different directions: More efficient systems, which are cheaper, eliminate redundancies, which provide resilience but cost more. For example, commercial airplanes always have two or more engines and have a co-pilot, even though one pilot and one engine is sufficient to fly the plane safely. The redundancy adds to expenses, but increases safety and resiliency in case something happens to one pilot or engine. In fact, commercial aviation is so safe because redundancy is mandated by regulation and built into every level, but our commercial-flying experience is so miserable because airlines have made it as efficient as possible to save money. (If one plane doesn’t arrive on time, there is no backup waiting to fly instead, for example.)