Students in most CS curricula have to make a wide variety of educational decisions including what courses to take. Frequently, they must make these decisions based on a very limited knowledge of the content of the topics they are choosing between. In this paper, I describe a theory of CS undergraduate course choices, based on 37 qualitative interviews with students and student advisors, analyzed with grounded theory. Most students did not have specific educational goals in CS and, as long as their classes were enjoyable, tended to assume that any course required by the curriculum had useful content (even if they could not articulate way). Particularly enjoyable or frustrating courses caused them to make long term course/specialization decisions and use a more strategic goal-oriented approach.