Fink, Begeer, Peterson, Slaughter, and de Rosnay (2014) conducted a prospective longitudinal study showing that theory-of-mind (ToM) development at school entry (mean age 5.61 years) significantly predicted friendlessness both concurrently and 2 years later. Friendlessness (defined as lacking any friendship that is mutually reciprocated) is conceptually and empirically distinct from group popularity and independently predicts adverse mental health outcomes throughout life. Here, we respond to the thoughtful commentaries by Wellman (Brit. J. Dev. Psychol, 2015; 33, 24-26), Mizokawa and Koyasu (Brit. J. Dev. Psychol, 2015; 33, 21-23), and Lerner and Lillard (Brit. J. Dev. Psychol, 2015; 33, 18-20) with a focus on three key issues, namely (a) the definition and measurement of friendship, (b) the measurement of advanced ToM development beyond the preschool years, and (c) the exciting future potential for ToM-based training and intervention studies to combat chronic friendlessness.