In the course of four short years, two unimaginable images have burned themselves into the minds of millions of Americans, images that have radically upset our collective perceptions about everyday realities, about being an American.

The first was the image of a passenger-filled jet plane being flown into one of the Twin Towers on an otherwise beautiful, cloudless September day four years ago. Like millions of people who saw this happen on television, I couldn't help feeling that I was watching a movie. Things like this don't happen in reality, right?

Of course, reality changed that day. The assumptions we had made about safety and security, about what could or could not happen in this country, were revealed to be just that — assumptions. Everyday experiences, such as being a passenger on an airplane or carrying a backpack on a subway in New York, would never again be the same.

The second image is a television shot of thousands of desperate people holed up in the New Orleans convention center after Hurricane Katrina blew through, waiting for someone in charge to get them out of there, or at least to restore order and bring food and water.

“We're Americans,” one of the trapped evacuees in the convention center angrily reminded the world as she spoke to a CNN reporter. Exactly. This kind of thing doesn't happen in America, right?

In all my years of writing about meetings, and in all the hours I've spent inside convention centers around the country, I never imagined I would see this image, or hear the truly strange phrase “convention center refugees.”

Convention centers were places where you walked miles visiting exhibit booths in cavernous halls, or sat in huge auditoriums and watched the video screens of speakers on stage telling you how to be a better this or a better that. They weren't places where people fleeing a storm ended up existing in squalor and fear for days, waiting to be rescued.

Katrina and 9/11. Who knows what else we will have failed to imagine before this decade ends.