I Hate These Straight Lines

Root cause analysis helps you solve a problem by helping you discover its most important causes. Many different methods and tools are used for this, but some of them are painfully inadequate. 5 Whys is one of those tools.

Pretend that the image below shows a problem and its causes. The problem is at the top, in the tip of the yellow area. Now follow the various branches down from the problem. The deeper you get, the more branches you have, and at the tip of every branch is something that acts as a cause. The problem actually happened because a whole bunch of causes came together in exactly the wrong way. This is what real problems look like if you investigate them thoroughly. There is no single, straight line of causation.

How will you solve this problem? One dumb way would be to try cutting off one or both of the major branches at a point just before the problem i.e. the "immediate cause" approach. Another less-than-smart way would be to eliminate one major cause at the end of the most obvious branch i.e. the "straight line" approach. Either of these might offer relief for a little while, but neither is likely to last long. All you really did, essentially, was try to dam the Mississippi River at the worst possible point or cut off one of many inputs. In other words, you'll accomplish nothing or force the river to find a new way to the Gulf... oh yeah, I thought this looked familiar.

So how could you solve the imaginary problem i.e. stop the Mississippi from draining into the Gulf?

• Remove or change some of the major causes i.e. endpoints?
• Place barriers to stop adverse cause flows before they become unstoppable?
• Change the system so that there are no adverse cause flows?
• Change the system so that separate adverse cause flows can't merge together? 
• Change the system so that the major flows can't head for New Orleans?!

Most of us don't have the ability to permanently stop the rain, dig major canals or tilt the North American plate so all runoff heads to Canada, so those last three solutions aren't going to work. That's not really the point of this analogy, though. The real lesson is that a single straight line cause analysis (like 5 Whys) is completely inadequate in many real world situations i.e. anything beyond the utterly simple.

If a problem looks simple enough that 5 Whys seems adequate, then you basically have one of the following scenarios:

1. you were taught that 5 Whys is adequate and you haven't questioned that claim, or
2. you have totally underestimated the difficulty of the problem, or
3. the problem never was very difficult to understand, or
4. you really don't care if the problem gets solved or not i.e. you're just doing a "root cause analysis" because somebody forced you into it.

In scenarios 3 and 4 you don't need a root cause analysis method that actually works, in scenario 2 the problem is more complicated than 5 Whys can handle, and in scenario 1 you are the problem. Scenarios 2, 3, and 4 show you that 5 Whys is generally unnecessary or inadequate. No amount of faith on your part is going to change that. You should ditch it and find something better.