Although mentorship is vital for individual success, potential mentors often view it as a costly burden. To understand what motivates mentors to overcome this barrier and more fully engage with their mentees, we introduce a new construct, "learning direction," which captures the beliefs people have about which individuals within a hierarchy-upward, lateral, or downward-are valuable sources of knowledge. Although most mentors believe knowledge resides higher up in hierarchies, the current research demonstrates mentors are more engaged and effective when they value insights from below. Our first three studies found that downward learning predicted mentor engagement (Study 1) because downward learning-directed mentors viewed mentoring as a worthwhile opportunity for their own learning (Studies 2A and 2B). A field study examined downstream consequences on mentees' learning outcomes, finding that downward learning-directed mentors trained more hireable mentees (Study 3). A final experiment established causality while also demonstrating that learning direction is open to intervention: reflecting on a downward learning experience increased mentor engagement, which enhanced the mentorship experience for their mentees (Study 4). We extend theories on learning orientation to learning direction and demonstrate that beliefs about the hierarchical sources of learning are critical to successful mentoring.