The Migration Decision
A newly promoted team lead has to move a payments service off a database that is six months from end-of-life. The fast path ships in three weeks and carries a known failure mode under peak load. The safe path takes eleven weeks and slips a quarter the whole company has committed to. Leadership is in the room, and the error budget is on the screen.
The team took the fast path and hit the failure mode in week two, during a sale. What made the decision defensible anyway was the rollback plan they wrote before shipping, and the single number they agreed in advance would trigger it.

