The first ‘why’ gets you to the proximate cause: there wasn’t enough time to complete the work.
The second ‘why’ uncovers what led to the proximate cause: Sally was expecting to get John’s portion of the work in 1 week but instead it took 2, which led to delays in her work.
The third ‘why’ unlocks yet another part of the causal chain: John received 3 deliverables from 3 different teams at the same time and in the midst of being overwhelmed he forgot to let Sally know that he needs more time.
This pattern usually continues until around the 5th ‘why’ where you get to the root of the problem — the thing that caused it all: teams are operating as silos and the lack of cross functional visibility is leading to an unsustainable rate of inbound work requests.
The difference between the 1st why and the 5th, 6th or even 7th ‘why’ is that instead of uncovering a symptom to treat again and again, you finally have enough information to solve the root of the problem and to make things better.