Cognitive studies focuses on how people understand and learn. It is still an amorphous field, and it is not yet really a single discipline. It overlaps many areas from anthropology to neurophysiology. It may not yet be "a science" as we in physics use the term, but developments in the past few decades have changed drastically what we know about how the mind works. The issue of how to teach physics is a difficult one: the attempt of a naive student to build a good understanding of physics involves many intricate processes over a long period of time. These processes tend to be much more complex than those most cognitive scholars have addressed. Nonetheless, some of the basic ideas of cognitive studies appear to be both firmly grounded and useful to the teacher of physics. The author briefly reviews some of the lessons he has learned from cognitive studies.