The first planning week of the year is when everybody is brave. Roadmaps are fresh, the release calendar has that new-calendar smell, and someone always puts “clean up the user table” on the board like it is a half-day task. Renaming a column sounds trivial. It is one line of SQL. What could it possibly do?
Quite a lot, as I learned on an otherwise ordinary release train. The rename itself took milliseconds. The rolling deploy around it took down nothing and broke something subtler: for about ten minutes, old pods and new pods were serving traffic against the same database, disagreeing about what a column was called. Nobody paged. The errors just quietly piled up in the logs until support started forwarding screenshots. That morning taught me the rule I have followed ever since: never change the schema in one step when two versions of your code will ever meet it.