One of the basic mistakes people do when it comes to lean implementations is rushing in the initial phases of the project and setting up unrealistic timelines and goals. People want to show instant results and convince the top managers and stakeholders. But they forget that the time spent on the drawing board is very important to the success of the project.
Every move in lean must be carefully planned. All the plans must be instrumented with required resources before the actual implementation. Plans must be communicated effectively to every levels of the organization. Everyone in the organization must know what their responsibility in the process is and especially why they do it. If this has not happened effectively, the project will not go far. Lean leaders must lead the way by example. They should not expect people to follow when they are not following the guidelines set with the new changes. They also must respect people and their talents in this process. All the people must be rewarded effectively for their efforts in the project and even after that.
All the moves in any lean implementation must be for the betterment of the entire organization. Critical mistake lean leaders make in lean implementation is trying to entertain higher authorities without looking at the benefits organization will get with those moves in the bigger picture. Simple yet critical mistakes like this will be recorded as lean failures, not as a failure of the project and methods used in implementations. I strongly believe most of the failures of lean are in this nature. They are failures of the projects rather than the failures of lean concepts.