Leverage

A pretty good description of how leverage made what may have just been a problem into a crisis.

And this doesn't even touch the subject of derivatives which Warren Buffet referred to as "financial weapons of mass destruction" way back in 2003. In that article he said: "The profits and losses from derivates deals are booked straight away, even though no actual money changes hand. In many cases the real costs hit companies only many years later."

In this case, many = 4.