Sure, you didn't. Let's start at the top, with new information first.
USA Today is reporting that NORAD was running exercises where aircraft, civilian and military, were hijacked and crashed into buildings for two years before September 11th, 2001. Interestingly the simulation of a crash into the Pentagon was scrubbed as "not realistic". That sounds like quite a few people had a good idea that planes might be used as weapons to me.
Also recently, it's been reported that the Hart-Rudman-Gingrich commision, which delievered it's report to the President twelve days after he entered office
Then there's the note that Attorney General John Ashcroft stopped flying commercial aircraft after the FBI warned him not to. I've mentioned this point before, and from the date on the article's byline (July 26th, 2001) it was noticed at the time. I find it really interesting that someone who tried to cut the counter-terrorism budget and changed the FBI's focus away from fighting terrorism would make that change lightly.