Going back to the previous version after a bad release. Rolling forward is the other choice: shipping a new version with the fix. Rolling back is usually faster, so you stop the harm first and fix it calmly.
How quickly you can undo decides how much risk each change carries. The trap is data. Code goes back and data doesn't, so one migration can quietly remove your way back, and you find out on the worst possible day.
Say it to your agent
“Before we deploy, tell me the rollback: the exact command, how long it takes, and what happens to rows written by the new version. If this migration makes that impossible, split it with expand and contract, so that going back works at every step. Then rehearse it on staging.”