There's simply no point in paying for Disaster Recovery (DR) if during a disaster it doesn't actually work!
That might sound ridiculous, but, frequently with DR systems that is actually the case. A quick google search will show you dozens of examples of big companies that have paid good money and the DR system has failed.
It all starts with proper planning, designing a DR solution that fits your recovery objectives, is realistic and within your budget.
Then, it must be actually tested or your DR system might be a disaster too.