Contemporary project-based organisations recognise the importance of leveraging past project knowledge for competitive advantage. By leveraging the lessons learned from previous and ongoing projects, organisations can benefit from managing learning within and across projects effectively. Despite these benefits, challenges persist in effectively reusing captured knowledge. This qualitative study addresses this gap by investigating knowledge reuse in project-based organisations, with a focus on social learning mechanisms. The results underline the pivotal role of collaboration and social interactions in facilitating tacit knowledge sharing and reuse, along with the significance of learning on the job. The research identifies drivers, barriers, and guiding principles for promoting knowledge reuse, addressing barriers such as motivation, resistance to change, and knowledge silos. Recommendations include establishing comprehensive databases, fostering collaboration, and strengthening Communities of Practice aligned with organisational goals. Moreover, the study emphasises that true organisational learning primarily occurs through social interactions, advocating for a shift from 'learning from repositories' to 'learning through social means.' It underscores the role of organisational culture, particularly trust, in enhancing learning and knowledge reuse, promoting personal networks, communities of practice, and blame-free cultures. Lastly, guiding principles advocate for both top-down and bottom-up approaches to foster knowledge reuse across all organisational levels.