Why must a method be repeatable

A method must be repeatable to determine or retry what you are testing for. For example: You find a cure to an outbreak. If what you're doing isn't repeatable, you would only have one cure and you would have no other way to discover or redo the steps to what made the cure. You would be stuck with that one vial of cure. Therefore, a method must be repeatable in order to reproduce and retry either steps, quantity, quality, or a task.