A review of the literature on the effectiveness of mentoring reveals a paradox: on the one hand, there is evidence that mentoring can be highly effective. On the other hand, meta-analyses usually only show small to moderate effect sizes, and sometimes even negative effects. To better understand this mentoring paradox, we discuss three fundamental problems in mentoring research. We propose working definitions and theoretical premises to overcome these problems. We apply various systemic concepts to the field of mentoring that might help to resolve the mentoring paradox. We introduce mentees' actiotopes and their interaction with other systems as the unit of analysis, and the regulations for which mentors are responsible for in the context of mentoring as the categories of analysis. To systemize and elaborate on the regulatory dimensions of mentoring, we introduce the nonagonal framework of regulation in mentoring (NFR-M). To facilitate the analysis of ongoing changes caused by mentoring and therefore a dynamic understanding of mentoring, we introduce the concept of spaces of possibilities in mentoring (M-spaces). Finally, we introduce the concepts of the Athena Mentor to explain why mentors can differ so dramatically in the effectiveness of the regulations they are responsible for in the context of mentoring. We conclude by describing how mentoring comparisons based on the NFR-M, mentors' regulatory insight, regulatory power, and M-spaces can help to resolve the mentoring paradox.