Evidence of nurse presenteeism has mainly focused on quantifying its prevalence and consequences on productivity, quality of care, and patient safety. Few data exist on nurses' perceptions of their presenteeism and its related causes. We explored concepts of presenteeism and its contributing factors with frontline nurses and nurse managers in different healthcare settings in Portugal and Switzerland. Our qualitative study design involved 8 online focus groups involving 55 participants. The transcribed data was explored using thematic analysis. Three main reasons for presenteeism were identified: unfamiliar terminology; the paradoxical effect of `being present' but absent; and presenteeism as a survival strategy. Six contributing factors were also recognized: (a) institutional disinterest toward employees; (b) paradigm shift: the tension between person-centered and task-centered care; (c) sudden changes in care practices due to the COVID-19 pandemic; (d) a lack of shared work perspectives with hierarchical superiors; (e) the financial burden of being absent from work; and (f) misfit of human responses. This study generates valuable, in-depth knowledge about the concepts and causes of presenteeism, and significant suggestions for the broader audience of nurse managers and leaders seeking to improve the quality of care.