Sampling error occurs when the participants selected for a study do not perfectly represent the broader population the research aims to understand, producing findings that deviate from the true population values. In research operations, managing sampling error is a core design discipline: sample size, recruitment method, screening criteria, and participant diversity all influence how far results can be trusted and generalised. Qualitative research does not eliminate sampling error but approaches it differently from quantitative work, prioritising depth and representativeness of perspective over statistical precision. Understanding the sources and limits of sampling error helps insights teams set appropriate confidence levels, communicate findings honestly to stakeholders, and design studies that are fit for the decisions they need to support.