A deploy performed by a person, on purpose, once a month

A fully automated deploy that nobody has run by hand in two years, and a rollback path nobody has exercised.

the practice, monthly:

  a real release, deployed by whoever is not on call,
  from the runbook rather than from memory, with the
  automation available and unused.

  what it found, over four months:
    the runbook referenced a host alias
    a sudo rule granted by hand in 2021
    the rollback command's flag order had changed
    nothing (month four)

month four is the goal and is not the point.

An automated path that works is not evidence that a human path exists, and the human path is what is needed when the automation is the thing that is broken. The cost is one deploy a month taking twenty minutes instead of four, which is cheap for the guarantee and is the first thing that gets skipped when a release is urgent.