Five nines uptime only exists in the mainframe world. Everywhere else it's a requirement set by someone in management, which is met by the vendor in their marketing material. It's never achieved over the long term, but enough time passes so the inevitable downtime can be blamed on the previous management. The vendor meets their "guarantee" by paying back less than a point on the yearly bill, and then everyone can reset the clock and pretend that it won't happen again.

The only people who suffer consequences are the staff forced to work overtime performing SEV0 RED ALERT theater. They will work through nights/weekends while the responsible parties tut-tut and "manage" by reading updates they can collate into the post crisis report. After that, everyone participates in the joy of emergency meetings to discuss said report that will be entirely worthless when a completely different part of the system fails the next time. A more reliable HA solution will be worked up by the engineers, finance will estimate implementation costs, and it will be turned down by an executive on the 8th hole green because they don't care about anything except improving profitability so they can hand themselves a bonus.

Not that I'm bitter or anything.