What is the best approach when it comes to teaching introductory quantum mechanics? Should students first learn how to do quantum mechanics, by doing numerous mathematical manipulations? Or should students start by understanding what quantum mechanics means? Perhaps we should do both. Then the question remains how the doing and the understanding fit together.
To answer these questions, the learning process of students has to be closely followed. In this paper problems are presented that have been observed in two introductory courses on quantum mechanics, one on quantum physics, and one on quantum chemistry. Some of these problems have already been described in literature. These observations form a starting point for future research on the learning of quantum mechanics.