And I promise that there are fail overs, simulations, testing, smaller issues, moving loads around, etc happening all the time behind the scenes. Getting caught out is no fun, but it's a very low percentage of the times when changing the tires on the bus driving down the freeway just goes [mostly] without a hitch.
You never notice all the times when the failover is executed smoothly with no interruption in service, just the times when something goes wrong.