It's the change that is the problem. Really. KM is only "hard" if the change from what is happening yesterday to what should be happening tomorrow is significant to the people expected to make the change. Now that I've said that, it sounds almost too obvious.
Malcolm Ryder at the Archestra blog is writing a series on Why Change is So Hard and already has a second installment, based on a reader comment to the first entry (which is quite good).
Malcolm used the term "alignment," and it pricked up my ears. I have been learning that alignment is critical and frequently more difficult than it sounds in theory. In the context of Malcolm's article, alignment has to do with the attitudes of people being affected by the change. But that isn't the only way alignment shows up. The change itself has to align with the goals and direction of the organization. And people involved need to understand how that change aligns with their perspective on the business. Malcolm provides a 2x2 matrix that suggests a direction for this.