This work examines the importance and value of relationships to learning and growth. I focus particularly on the importance of fostering and supporting friendship between persons with differing life experiences -- friendship across diversity. Rooted in the work of John Stuart Mill and Chimamanda Adichie, I claim such friendships provide a foundation not only for learning, but also for creating knowledge in the world. As a case study, I examine friendship between women and men in contemporary American society. I claim such friendship is a vital, yet under-supported, aspect of our development, as individuals and as members of a pluralistic society. In light of the potential benefits of friendship across difference, I advocate developing ways to increase societal support for such friendship and suggest how we might do so, in education and in wider society.