This research paper uses system justification theory (SJT) as a lens to understand stakeholder resistance during an Enterprise System (ES) implementation project. A case study is presented involving a problematic ES implementation illustrates the efficacy of SJT in this respect. The findings show that SJT explains a number of features of stakeholder resistance. Firstly, SJT makes comprehensible the tendency of stakeholders to vigorously defend established systems on which they feel they depend. Secondly, the theory explains and predicts the tendency of system defenders to attack not just the features of the new system but the advocates of the new system as well. Third, SJT predicts the tendency of stakeholders to switch allegiances when the new system is seen to be inevitable. Finally SJT explains the emotional and non-rational nature of some resistance behaviours. The paper concludes with some practical implications of SJT for the project management of ES implementations.