This is rahter simplified. What brings large companies down is always a mix of things that go wrong. There are external factors that come into play, and will affect your organisation no matter how well prepared you are.

As an example one of the largest banks in my country has always acted responsibly, never done anything without careful consideration, and not been involved in the whole subprime mess. Yet because of external factors (in this case bad management of other banks) their stock went down 30% in three days and they were probably on the brink of bankruptcy.

Whether you act small or not as a large company it will not insulate you from external factors that you have no control over. The best you can do is to have contingency plans, which large corporations are extremely good at.