Characterizing the initial state of students is the province of education, cognitive psychology, and the emerging fields of specific subject-matter education, including physics education. If every learner were in a completely unique state, it might be impossible to implement a finite number of operations to substantially populate any desired final state. Luckily, broad categories have been found which categorize the initial state of a large fraction of people. This characterization of the initial state of the learner has improved dramatically over the last 20 years and a more precise characterization will come with the increase of research support and the development of new diagnostics tools. As in physics, random guessing is not an efficient technique, although it sometimes works.
Theory is needed as a guide, and it is provided by the fields of education and cognitive psychology.
A theory does not have to be correct to prove useful. After all, caloric theory was useful in guiding the early and very fruitful development of thermodynamics, and Newtonian theory is still useful in many venues. A useful theory can encompass basic principles or be purely phenomenological. It begins with the observation that apprenticeship has been an effective approach to teaching complex skills in a small group setting, and then extends that approach into the realm of more abstract learning for large numbers of people. This provides the necessary framework to teach a course, and the framework, in turn, provides a structure to help teachers incorporate other empirical observations.