How to convince your manager with a door handle?

“How much time do you need to test this? “ my manager demanded.
“I cannot give an estimation, because I do not know, how it has been corrected.”
Annoyance came in her voice:
“Han Toan, what are you talking about?”
A pressing silence followed.

I looked around for a simple object to make my message clear. A powerful trick I learned from a senior business consultant. My eye fell on the door.
“Suppose, that this door handle had been broken. The supplier fixed it.”
She nodded slightly.
So I continued: “What would you test, if they only replaced the door handle?
The door? The room? The floor? The wing? The building?”
The atmosphere changed in the room: she understood it.

At that moment I did not need to use plan B:
“If the building has been replaced, would you test the structure of the building before testing the door handle?
If the complete wing has been replaced, would you check the water pipes and electrical wiring before testing the door handle?
If the door has been replaced, would you also check the lock?”