ByTim McMahon via aleanjourney.com Article
“‘A relentless barrage of ‘why’s’ is the best way to prepare your mind to pierce the clouded veil of thinking caused by the status quo. Use it often.’ — Shigeo Shingo
A brilliantly simple root cause problem-solving tool, asking why five times becomes easier the more you do it. Adopting this as a default way of looking at things will aid, not only your problem solving, but other areas, too. Ask the Five Whys to get beyond the obvious symptoms to discover the root cause.
Taiichi Ohno gave this example about a machine that stopped working (Ohno 1988, p. 17):
1. Why did the machine stop?
There was an overload and the fuse blew.
2. Why was there an overload?
The bearing was not sufficiently lubricated.
3. Why was it not lubricated?
The lubrication pump vs not pumping sufficiently.
4. Why was it not pumping sufficiently?
The shaft of the pump was worn and rattling.
5. Why was the shaft worn out?
There was no strainer attached and metal scraps got in.
Without repeatedly asking why, we would likely replace the fuse or pump and the failure would recur. Keep asking why until the root cause is reached and eliminated.
Test your 5 Whys chain with the ‘therefore’ test. Start at the bottom of the chain and say Last Why occurred, therefore the second to last why occurred. Carry on until you reach the first why. If it isn’t true, revise the why chain until you can pass the ‘therefore test’.”