The learnings from 9/11

The report of the 9-11 Commission (more formally, The National Commission on Terrorist Attacks Upon the United States) is available online. The report, which spreads blame across two administrations, uses language that's a welcome deviation from the constipated prose one usually gets from such bodies. It features section headings like: Chapter 1: "We Have Some Planes" and Chapter 7: The Attack Looms and Chapter 8: "The System Was Blinking Red".
Here's the intro to Chapter 11, FORESIGHT—AND HINDSIGHT

In composing this narrative, we have tried to remember that we write with the benefit and the handicap of hindsight. Hindsight can sometimes see the past clearly—with 20/20 vision. But the path of what happened is so brightly lit that it places everything else more deeply into shadow. Commenting on Pearl Harbor, Roberta Wohlstetter found it “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.”
As time passes, more documents become available, and the bare facts of what happened become still clearer. Yet the picture of how those things happened becomes harder to reimagine, as that past world, with its preoccupations and uncertainty, recedes and the remaining memories of it become colored by what happened and what was written about it later. With that caution in mind, we asked ourselves, before we judged others, whether the insights that seem apparent now would really have been meaningful at the time, given the limits of what people then could reasonably have known or done.
We believe the 9/11 attacks revealed four kinds of failures: in imagination, policy, capabilities, and management.