Changing an aeroplane in flight
The defining constraint of process redesign is that the process cannot stop. Customers keep arriving, work keeps flowing, and the team is expected to maintain output while the ground moves.
That rules out the approach people naturally reach for, which is to design the new process fully, then switch. Big-bang cutover concentrates all the risk at one moment, and the failure mode is severe: if the new process does not work, you have already dismantled the old one.
What works instead is incremental introduction with the ability to reverse each step. Three properties make that possible.
Each change is small enough to attribute. If three things changed and the result got worse, you cannot tell which caused it, and you will probably revert all three including the one that helped.
Each change is reversible for long enough to matter. The old path stays available until the new one has been observed under real conditions including a busy period.
And each change is measured against the baseline from the first lesson, which is the only reason any of the observations mean anything.
The temptation to move faster is strongest when the redesign looks obviously right on paper. That is precisely when the discipline pays, because obviously right designs fail on details nobody modelled.

