Abstract
The paper summarises previous theories of accident causation, human error, foresight, resilience and system migration. Five lessons from these theories are used as the foundation for a new model which describes how patient safety emerges in complex systems like healthcare: the System Evolution Erosion and Enhancement model. It is concluded that to improve patient safety, healthcare organisations need to understand how system evolution both enhances and erodes patient safety. Significance for public healthThe article identifies lessons from previous theories of human error and accident causation, foresight, resilience engineering and system migration and introduces a new framework for understanding patient safety in healthcare; the System Evolution, Erosion and Enhancement (SEEE) model. The article is significant for public health because healthcare organizations around the world need to understand how safety evolves and erodes to develop and implement interventions to reduce patient harm.