It is much easier after the event to sort the relevant from the irrelevant signals. After the event, of course, a signal is always crystal clear; we can now see what disaster it was signaling, since the disaster has occurred. But before the event it is obscure and pregnant with conflicting meanings. It comes to the observer embedded in an atmosphere of “noise”, i.e., in the company of all sorts of information that is useless and irrelevant for predicting the particular disaster.
― Wohlsletter, 1962 Pearl Habour: Warning and Decision, quote in Silver, The Signal and the Noise