The magic insight is always this: "Because I want to feel good." When someone doesn't want to put this in words, they get annoyed and stop talking to you.

You're so right... but you can substitute "powerful", " secure", etc for "good"; and also sometimes "because of secret reasons".

Sometimes it's, "Because I don't want a repeat of this crappy thing that happened to me."

Often software is used as a means for one group inside a company to control another group.

Part of the idea is that if it takes more than 3 or 4 "why"s to get to some really fundamental business goal (i.e. "Because I want to make more money"), then it might not be a problem worth solving in the first place

What if you told them ahead of time what you were doing, so they would happily cooperate knowing there would only be 5? Otherwise, by the fifth most people will think "man, this never ends..."

I'd probably ask "Why 5 times?" and then it would be game on.

By six, you're usually at something like "because that makes me happy". By seven, you're into metaphysics and cognitive science.

Of course, some issues are genuinely simple, and you're off in unhelpful territory halfway through. I suspect five why's is a decent estimate, but not necessarily more accurate than four.

There's a really good Louis CK routine about this, involving his young daughter.

"Diminishing returns."