Even the big dogs go down...
Last week facebook, one of the biggest dogs in the dog park, was down for quite some time. Trying to navigate to the page yielded a connection time out. Was this a network operations mistake, network problems, or server issues? I am not sure what the cause of the outage was, however there were many disgruntled users being quite verbose on twitter and other social networking sites.
Other major players such as Netflix also experience downtime every so often. A major outage happening during the Christmas holiday 2012. It just goes to show, that no matter how large and how much infrastructure and redundancy you have, it's likely that you will experience some down time once in a blue moon.