Taiichi Ohno, the architect of the Toyota Production System in the 1950s, describes the method in his book Toyota Production System: Beyond Large-Scale Production as “the basis of Toyota’s scientific approach . . . by repeating why five times, the nature of the problem as well as its solution becomes clear.”
Ohno encouraged his team to dig into each problem that arose until they found the root cause. “Observe the production floor without preconceptions,” he would advise. “Ask ‘why’ five times about every matter.”
Which is great. But when taking the 'why' dive in consumer research, stop asking why before you get to "because it makes life better" as the answer. All 'why' question probes with consumers ultimately lead there--from socks, to cheese, to cars, to snow blowers. So 'making life better' isn't your unique root insight.