Failure to plan is planning to fail.
We've all heard the old adage, but with software, failure should be part of any plan. This isn't because we want or even know that failure will occur. We certainly don't want the application to fail, but disaster happens. It could be a fire at the data center where the application is housed, infiltration by a malicious hacker, or any number of things that cause an application to fail. What's important, though, is that you have a plan in place to get back up.