This paper describes the use of activity theory to compare dissimilar cases in a study of adult online music learners. The purpose of the study was to better understand the barriers that keep self-motivated users of online open education resources from experiencing successful independent learning. Eleven participants were given tutoring-style help in pursuing their goals, which involved conceptual music learning, with the aim of understanding and overcoming the barriers they had encountered. The use of activity theory in the data analysis revealed underlying issues that connected self-motivated learning projects that were markedly dissimilar. Study findings are detailed elsewhere; this paper focuses on the usefulness of activity theory as a lens for understanding and comparing cases of individual learning.