For those still a little bit baffled by how the credit crisis started and then snowballed I recommend you spend 11 minutes watching this video. The concepts are very simply explained including: leverage, collaterised debt obligation and sub-prime. The knowledge will help you become a better investor in the future so that you can better understand the true risk of your investments.
Much kudos to creator Jonathan Jarvis. You can also visit the official website for the videos.
The Crisis of Credit Visualized from Jonathan Jarvis on Vimeo.