Continuity Plans or Systems

A friend asked myself why we(AdvGen) always recommend all of our clients have some Continuity Plans or Systems if their IT system is essential for their business. She said if all go well, there should be not any problems. I asked her what if something goes wrong, they may lose money or clients. We cannot assume the things go well. This is not a prefect world, if anything can go wrong, there is possible to go wrong. Thus, we have to assume the worst situation can happen, how we can deal with that.