Good post, Peter.
In addition to that lag between the discovery of the principles and their practice, and the fact that the application of the principles is a different activity with different skills, there is also the complication of the conflict with opposing views. When you are at war (so to speak) you become preoccupied with firing and ducking and it can take one away from transitioning to applying the principles.
I also suspect that we underestimate the time it takes to really learn new principles and that when we attempt to apply those principles that aren't yet well understood or fully integrated, the practice is poorly done.
Medicine, which you mentioned, has theory, practice, and technology, also has research - to measure, explain and evaluate. Objectivism is the theory, and we know a little about the practice (reason, individualism, protection of individual rights - in some context or area) but the missing technology and research may be something like the comparisons that could be made between private schools as a context (if we had free choice in a totally privatized school system). In Medicine, the application of theory requires a technology, BUT without an objective study of the results following the practice of a given technology, everything would be as much dogma as reason. As the movement at the state level to convert to a very full voucher system goes on, we might have the integration of theory, technology, practice and research. And sometimes the most cogent explanation of a theory comes from the explanation of the research results (a special kind of hindsight).
There is also "purpose" (motivation) and the fact that we move forward in theory before we have a very rich understanding of practice. We had no clue what kind of uses personal computers would be put to when the theory, and the technology they required, came together. People were excited about having a personal computer, but were clueless as to what purpose they could be put to ("You can store your recipes on your home computer!" Or, "Keep a list of all of your record albums!") I know that people have a hard time explaining the personal, economic and political benefits of Capitalism in a way that paints an exciting vision of the future to the average listener. Sure, you can always get the political base excited with hot-button phrases, but how to paint a picture for the average person.... a picture that makes it purposeful to adopt limited government is harder to do.