How can your credit score negatively affect you?

If you should some day wish to borrow money for some reason, such as for example, to get a mortgage for a house, the bank will only lend you the money if they believe that your credit rating is good enough. I realize that this may sound silly in the age of the sub-prime mortgage crisis, but at least in theory, that's the way it works. In practice, the banks may lend you money anyway.