Five Whys is “a question-asking method used to explore the cause/effect rela­tion­ships under­ly­ing a par­tic­u­lar prob­lem. Ulti­mately, the goal of apply­ing the 5 Whys method is to deter­mine a root cause of a defect or prob­lem”. Devel­oped by Tai­ichi Ohno–one of the inven­tors of the Toy­ota Pro­duc­tion System–the oft-cited exam­ple is as follows:

  • My car will not start. (the problem)
  1. Why? — The bat­tery is dead. (first why)
  2. Why? — The alter­na­tor is not func­tion­ing. (sec­ond why)
  3. Why? — The alter­na­tor belt has bro­ken. (third why)
  4. Why? — The alter­na­tor belt was well beyond its use­ful ser­vice life and has never been replaced. (fourth why)
  5. Why? — I have not been main­tain­ing my car accord­ing to the rec­om­mended ser­vice sched­ule. (fifth why, root cause)

I was intro­duced to Five Whys in a post by Joel Spol­sky back in early 2008 detail­ing their post-mortem exam­i­na­tion fol­low­ing a sys­tem out­age (which also looks at the prob­lems with SLAs).

Entre­pre­neur Eric Ries recently wrote a com­pre­hen­sive post detail­ing how to con­duct a Five Whys root cause analy­sis which I sup­pose acts as an update to this pre­vi­ous post of his where he intro­duces his read­ers to the Five Whys con­cept and adds this impor­tant caveat:

The next step is this: you have to com­mit to make a pro­por­tional invest­ment in cor­rec­tive action at every level of the analy­sis.

Five Whys is a con­cept I’ve attempted to–somewhat successfully–apply to myself and my devel­op­ment. When I make mis­takes or when I don’t under­stand some­thing I ask why until I find the root cause of my error, the mis­un­der­stand­ing, or the neg­a­tive reac­tion. Sim­i­larly, GigaOM’s Mike Speiser rec­om­mends Five Ways as one of the four tech­niques you should embrace in order to become at ease with ideas that make you uncom­fort­able.

You may find that your reac­tion is more about pro­tect­ing exist­ing ortho­doxy or the source of the idea than it is about the mer­its of the par­tic­u­lar approach at hand.

And of course, to end in a joke, you don’t want to ask why too many times (via Kot­tke).