When I worked for the Winter Olympics in Vancouver, it was pounded into our heads all the time that there was no second chance. Everything we did would get one chance only.
For that reason, we had two Technical Rehearsals. The purpose was to test both our systems and our procedures, and identify how they could be refined for the real thing. It was someone's job to actually design a huge number of expected and unexpected issues so that tech operations teams at each venue could be tested as to their response. Issues ranged from broken printers to network meltdowns to broadcasting failures, etc. We had two Technical Rehearsals for hopefully obvious reasons. And before the Technical Rehearsals, we also had the test events (i.e. world class but lower profile sporting competitions held at the Olympic venues to see whether we fell short in putting up a world class competition event).
We also had Disaster Rehearsals to test our disaster recovery systems and procedures, though I wasn't personally involved in those. I did get a string of text messages when it was happening though. "Primary datacentre flooding, starting emergency processes to switch to secondary datacentre now." etc. Never mind that nobody could ever believe that the primary datacentre could get flooded in a million years. The attitude was that any disaster was possible, and we had to prepare for the impossible.
If you have one shot only, and that shot is important, you need to have a large process committed to making sure that one shot goes well. And that process needs to be managed by someone experienced in that type of thing.