The logic of tsunami-tendenko: Super-rationality in the Altruist’s dilemma

“Tsunami-tendenko” is a moral handed down in a local area of Japan. It says that we each should evacuate from tsunami separately as individuals, starting as early as possible, in haste, and without caring for others. The imperative may seem counter-intuitive at first glance. I tried to elucidate the logic in tsunami-tendenko by constructing a symmetric two-person two-alternative game of evacuation, which is formulated as an example of the Altruist’s Dilemma, and showing that we can interpret the moral as the super-rationality solution to the game. I also examined the implications of the argument, focusing on the scope of tsunami-tendenko on the one hand, and the significance of general trust and deliberation in practicing it on the other hand.