This study aims to provide insight into individual teachers' behaviour and decisions regarding the exchange of knowledge, focusing on status, interdependence and reciprocity, and psychological safety. It highlights the key role of the individual professional in knowledge-sharing and professional development contexts. A social-constructivist perspective and qualitative design (case study) were employed. Eighteen teachers in upper-secondary vocational education were questioned in interviews or focus groups. Data was analysed by coding, interrelating, and reasoning. Results show how professional discretion directs intercollegial communication and sharing. Interpersonal issues (status, safety, and reciprocity) influence decisions about sharing with or withholding knowledge from certain colleagues. Consequently, professional development and processes of sharing and managing knowledge are in danger of falling flat when ignoring the individual's impact. This emphasises the importance of individual professionals' attitudes and preferences, and informal, social structures in approaches to professional development, knowledge-sharing practices, and learning communities.