Background <p>Human factors (HF) are integral to patient safety. Simulation-based education (SBE) is widely used to teach HF, yet facilitators conceptualise HF in varied ways. This study explored facilitators’ conceptions of HF.</p> Methodology and methods <p>A qualitative phenomenographic study was conducted with 12 SBE facilitators from diverse professional backgrounds. Purposive maximum-variation sampling sought participants from different professions, simulation roles, and educational contexts. Semi-structured interviews were conducted via Microsoft Teams, transcribed verbatim, and analysed iteratively to identify categories of description and an outcome space capturing qualitatively different conceptions.</p> Results <p>Four conceptions of HF were identified: (1) HF as a patient-safety science, (2) HF as human-to-human interactions, (3) HF as optimisation of individual performance, and (4) HF as reducing error (‘To Err is Human’). Participants sometimes drew on more than one conception, but usually foregrounded one dominant way of understanding HF. The conceptions differed in scope and alignment with HF theory rather than in simple legitimacy. Dimensions influencing conceptions included professional experience, simulation pedagogy, continuous professional development, and approaches to measuring educational quality.</p> Discussion <p>SBE facilitators hold heterogeneous conceptions of HF, risking inconsistent educational practice. In phenomenographic terms, broader conceptions encompassed aspects visible in narrower ones; this should not be read as a claim that one conception is always the ‘best’ for every simulation objective. Rather, different educational aims may legitimately foreground different aspects of HF, while systems-informed conceptions align more fully with contemporary HF science. Clearer definitions, stronger faculty development, and closer collaboration between simulation educators and HF specialists may enhance educational design and patient-safety outcomes.</p>