I usually checked news online at work first thing, in our small office, but that morning I had not. We lived on the west coast, so the events had already happened (or were still unfolding) and I was unaware. A colleague in Europe reached out to me, basically just saying "it's horrible, horrible," and I had no idea what he was talking about. Didn't get a lot of work done that day. I seemed to be a lot more optimistic than some about our prospects in the wake of the attack, and was not particularly paralyzed for days and days. Probably I repeat this every year, but I do remember that the identity of the attackers wasn't made known publicly for a while, and I was thinking it could be the Chinese embarking on some gambit; something less than a nuclear attack, leaving the administration with some difficult decisions on a proportional response. "Yeah, that was us. Now about Taiwan..." Glad I was wrong about that, bad as it was. Afghanistan seemed a more manageable adversary.