Entropy tends to a maximum.
Now guys, remember the third law of Thermodynamics - "entropy tends to a maximum" or to put it another way - "Things get worse."
You can do all the testing that's practically possible, and run it in development and testing systems before putting it live, but it can still go bad. You need to be prepared for that to happen in spite of all your efforts, and to be able to back out to the state that last worked happily with minimum outage.
And IF that all goes wrong, YOU NEED CALM, CAPABLE, EXPERIENCED TECHNICAL STAFF WHO UNDERSTAND YOUR SYSTEMS, WHO CAN THINK AND COLLABORATE TO SAVE YOUR BACKSIDE.
Would you travel as a passenger in a plane that was being flown by a cut price pilot who had never flown that kind of plane before? Just remember that pilot who crash landed with his passengers and crew on the Hudson River in New York.
"that's why we test the change & backout in as close to live as possible, the day before we do any changes." Good, you'll go far.
"they cannot have followed dev, test prod and therefore that's a FAIL, not an accident," Uh ohh, you need more experience of the real world. It just ain't as easy as you think it is.