This happens all the time. Every single thing that you see in software development happens in network engineering and data center engineering, except that where in development in general senior people who write software are capable of at least guestimating complexities to provide a marginally unified front against the unreasonable expectations of execs, it is pretty much never the case in neteng or dcops as those that develop software cannot write their heads around the complexities of working with physical hardware.

It is rather counter-intuitive. In neteng and dcops, "I don't know and I cannot find out. I can only attempt to mitigate what i think might have caused it for next time" is a very reasonable answer to 99% of the "why this happened?" questions because in order to replicate the situation to test the theory one needs to recreate the same problem again on the same scale.

This also means that certain things cannot be tested. Most of generator tests are garbage - turning on generator and running it without production load delivered over the transfer switch does not test anything other than that one can turn on a generator and run it. The problem typically happens not because the generator ( also is there the generator or the first and the second generator? Why is there no generator bank for a non monkey-sized company? ) does not start - the problem is because over time transfer switch develops a problem and unlike generators it is not possible to test a transfer switch where in the event of a test failure the customers won't lose power unless the data center is designed from the beginning to deliver A and B powers over separate circuits to every single customer and every single customer has per system ( not per rack ) transfer switches.

Of course it costs a lot more money, something that companies are reluctant to spend.