Most objective functions assume that the probability distributions have short tails, and few probabilistic models provide accurate representations of long tails: Newton’s laws of mechanics assume that an object does not move too fast, and most objects comply with the assumption.

Occasionally long tails matter. Negative consequences of a highly improbable event outweigh benefits of good behaviour in an average case. A model in which very rare events are neglected leads to designs optimized towards wrong goals; but discovering and analyzing a model which takes care of rare but harmful disasters properly isn’t easy.

Since long tails are difficult to handle, they should be avoided. Chances of rare bad luck grow with the complexity of design: an iron hammer with a wooden handle is slow in application, but almost nothing can inpair its ability of hitting nails. On the other hand, an electronically controlled high power nail gun is very efficient, but a failure in the electronic circuit renders the tool useless.

Speed, resource consumption, ergonomics are important most of the time; but simplicity is the only reliable mean to achieve robustness — the promise that a tool or a system remains usable when things go wrong.

The vaccine immunizes but can cause complications, even death. The vaccine worsens the patient’s condition if the patient is both infected and vaccinated at the same time. The vaccine stops the flu from spreading, if enough people are vaccinated. If enough people are vaccinated, the patient should not be vaccinated since the infection stopped spreading.

Thus, if everyone is just like everyone else, there is no pure strategy equilibrium, and the patient should throw a coin to choose whether to take the injection. On the other hand, if some are more equal than others, they can skip on the vaccine and let others suffer for their good.

Only computer scientists understand why a pure strategy exists if computer scientists behave differently from normal people. So, the pure strategy is to vaccinate everyone except for computer scientists.

Flawless, isn’t it?