From the end of Chapter 7 ("Surprise") of Roberta Wohlstetter's Pearl Harbor:

This study has not been intended as a "how-to-do-it" manual on intelligence, but perhaps one major practical lesson emerges from it. We cannot count on strategic warning. We might get it, and we might be able to take useful preparatory actions that would be impossible without it. We certainly ought to plan to exploit such a possibility should it occur. However, since we cannot rely on strategic warning, our defenses, if we are to have confidence in them, must be designed to function without it. If we accept the fact that the signal picture for impending attacks is almost sure to be ambiguous, we shall prearrange actions that are right and feasible in response to ambiguous signals, including signs of an attack that might be false. We must be capable of reacting repeatedly to false alarms without committing ourselves or the enemy to wage thermonuclear war.

It is only human to want some unique and univocal signal, to want a guarantee from intelligence, an unambiguous substitute for a formal declaration of war. This is surely the unconscious motivation of all the rewriting of Pearl Harbor history, which sees in such wavering and uncertain sources of information as the winds code and all of the various and much-argued MAGIC texts a clear statement of Japanese intent. But we have seen how drastically such an interpretation oversimplifies the task of the analyst and decisionmaker. If the study of Pearl Harbor has anything to offer for the future, it is this: We have to accept the fact of uncertainty and live with it. No magic, in code or otherwise, will provide certainty. Our plans must work without it.

^z - 2017-12-19