Background The concept of ‘positive thinking’ emerged in cancer care in the 1990s. The usefulness of this approach in cancer care is under increasing scrutiny with existing research, definitions and approaches debated. Nurses may wish to judiciously examine the debate in context and consider its relevance in relation to their experience and clinical practice. Purpose To offer a constructivist perspective on ‘being positive’ we extract data from a constructivist grounded theory study on humour in healthcare interactions in order to identify implications for practice and future research. Methods We present three areas for consideration. First, we review the emergence of this concept in the broader context of health care generally and cancer care specifically. Second, we present data from a grounded theory study on humour in healthcare interactions to highlight the prevalence of this aspect of cancer care and its contested domains. We conclude with implications for practice and research. Findings Patients actively seek meaningful and therapeutic interactions with healthcare staff and ‘being positive’ may be part of that process. Being positive has multiple meanings at different time-points for different people at different stages of their cancer journey. Patients may become ensnared by positivity through its uncritical acceptance and enactment. Conclusion Positive thinking does not exist in isolation but as part of a complex, dynamic, multi-faceted patient persona enacted to varying degrees in situated healthcare interactions. Nurses need to be aware of the potential multiplicity of meanings in interactions and be able (and willing) to respond appropriately.