The habit of repeatedly asking yourself the enabling question as soon as you encounter a problem. That way you get beyond the visible symptoms and get to the root causes of a problem. 

Taiichi Ohno illustrates the operation of 5×waardoor using this example about a machine that no longer works (Ohno 1988, p. 17): 

1. What caused the machine to stop? It was overcharged and the fuse blew. 

2. What caused it to be overloaded? The bearing was not lubricated well enough. 

3. What caused the bearing not to be lubricated? The lube pump was not pumping properly. 

4. What caused the lube oil pump not to pump properly? The shaft of the pump was worn and rattled. 

5. What caused the shaft to wear out? There was no filter on it, so metal shavings got into it.... 

Managers who do not ask themselves the making question several times only replace the fuse or pump, after which the error reoccurs. The number five is arbitrary. It's more about continuing to ask until you get to the root cause and can eliminate it.