One of the most basic fundamentals in the lean approach to business is the single biggest barrier preventing the majority of business "getting it". It can be simply put just like the title of Jim Womack and Daniel Jones' book, it's all about "Lean Thinking".
As Dr. Shigeo Shingo stated, "much more than a matter of technique; it is an entirely new way of thinking about production itself". That's our problem. We don't think lean, we just use the tools..sometimes.