Our marketing materials describe our training as fast-paced and challenging. But Kathy Sierra writes a much better description in her blog:
You can’t create new pathways in someone’s head… your job is to create an environment where the chances of the learner ‘getting it’ in the way that you intend are as high as possible.
Creating Passionate Users: Crash course in learning theory
In other words, you have to hold a learner’s interest and make them think. Read the whole entry, especially if you are responsible for delivering knowledge via training, documentation, or any other communication.