Previous studies investigating proximity and collaboration have not clarified personal elements, such as working or communication style. Here, we show that personal proximity-close similarity in terms of personal traits and behavioral patterns-substantially affects the whole life cycle of research collaborations. We conduct a multi-case study of Dutch nanotechnology researchers. We select our interviewees through a bibliometric analysis and focus on the most central Dutch nanotechnology researchers in the global network. Our results reveal that social proximity and temporary geographical proximity have indirect effects enabling potential partners to assess their personal proximity. Sufficient levels of personal proximity often make or break the deal, provided that partners' cognitive and organizational proximity-which are major drivers of research collaborations-suffice. Introducing personal proximity to analyze research collaborations puts previous findings on proximity dimensions' effect on collaboration in a new perspective.