Like a catapult

Why is the current housing/mortgage crisis like being shot out from a catapult?

There are several ways:

1. The damage is really done during the ride up - but it's only recognized once you start down.
2. Once you're launched, it's really, really hard to see how it's going to end well.
3. And if you don't know what's coming at the end, the ride up can be pretty exhilarating.

The lesson here is that it's going to be nearly impossible to stop all this from unwinding - the time to do that was before we climbed on to Greenspan's catapult.