Purpose Most complex engineering projects encounter unexpected events through their life cycle. These are traditionally attributed to inaccurate foresight and poor planning. Outlining a nonanticipatory alternate, the authors seek to explain the ability to rebound from unexpected events, without foresight, using resilient systems theory. This paper seeks to outline the theoretical underpinnings of project resilience and to identify criteria for planning and selecting projects for greater resilience. Design/methodology/approach Investigating project resilience, this paper studies the relationship between unexpected events and project performance in 21 projects. The authors perform a systematic review of project ex post evaluations 3-12 years after project completion. Findings First, the authors find that all projects encountered unexpected events, even when discounting planning error. Second, the authors show that, as a consequence, projects underperformed, not necessarily relative to formal criteria, but in terms of subjective opportunity cost, that is, relative to competing alternates - known or imagined - foregone by their implementation. Finally, the authors identify four types of resilient projects - superior, equivalent, compensatory and convertible projects - as opportunities for building project resilience. Practical implications The properties of resilient projects provide opportunities for building resilience in complex projects. Originality/value Departing from traditional efforts to "de risk" plans and "de-bias" planners, this paper focuses on the properties of projects themselves, as an alternate to improved foresight and up-front planning.
