Skilled people failing. This is what many lean transformations look like. Why? The rules are changing. Bosses with hammers find that leading their organization now requires a Swiss army knife. What got you here won't get you there. This is a topic that has been covered extensively under the mindset change, behavior change, organizational development, lean leadership topics. Exit the comfort zone into the learning zone, but not too far into the fear zone. Etc.
But let's talk about skilled consultants failing. Specifically lean consultants. What's our excuse? Trick question. Lean people don't make excuses. We ask why and seek causes. I'll put incompetence aside for the moment since the causes and countermeasures to that are well known. Caveat emptor. Where competent and skilled consultants often fail is when entering domains in which there is a high degree of uncertainty, with a high degree of certainty that they know what they are doing. There is also a remedy for that. For those new to the notion of humble inquiry or it's two individual elements, I recommend this book.
Lately I've recognized what may be a pattern among skilled lean consultants failing. We can call it luck / bad luck, bad fit with the client, but to be more scientific it is a case of being unable to recognize the context switch from certainty to uncertainty. Just as leaders who can't switch between directive, supportive, delegating and coaching styles have limited long-term success, consultants need to read the environment skillfully and sometimes stop being the sensei, the coach, the roll-up-your-sleeves-and-move-the-machine guy, or whatever style is not appropriate for the specific client environment.
It's hard to say "recognize when you are in an environment that doesn't suit your default style" because people tend to be blind to these things. As a more general rule, consultants can begin by recognizing that there are almost always invisible factors which have a large effect on the successful outcome of the project, transformation or intervention. Root these out, question assumptions, be nervous if things are going too smoothly for too long. If wins are coming early, fast and easy, question whether you really understand cause and effect. Luck turns. True skill recognizes this.
Skilled lean consultants are in the business of selling effective change. The content has been fairly stable over decades, maybe centuries. The context is constantly changing. How well do you recognize this?