Several days ago a colleague was sharing how he bumped into Bob, his initial sensei (and mine) at the airport. My colleague told Bob that he thinks of him every day when he coaches his clients - "What would Bob do?" Not that we need to be handing out WWSD bracelets, but we should all think, "What would the sensei do?"
Of course, it depends on your sensei. Bob is lean Hall of Fame good. He started his lean journey as VP of Ops at Danaher's Jake Brake in 1987, the veritable U.S. lean beachhead. Now, if you have any questions relative to the quality of your sensei, then perhaps ask, "What would Ohno do?" Not a bad choice.
So, when should you apply WWSD and on what should it make you reflect? I think WWSD is really a situational thing and has less to do with lean tools and more to do with lean principles and systems and lean transformation leadership. That's where we usually get into trouble.
For example, when we encounter concrete heads and waffle about things like flow, pull, scientific thinking, integrating improvement with work, respect for the worker and bias for action, we can really screw up a lean transformation. We can end up directly or indirectly teaching people that lean principles are subjective. Not a good thing!
So, think about your sensei and the lessons that he or she has imparted to you. How and when do you (should you) apply WWSD?