In the fourth of an eight part series on the humble project management toolkit for better results in an uncertain world, I describe the second of two major causes of the ‘Planning Fallacy’ (why projects go over budget, over time, and fail to deliver according to specification… over and over again): - Complexity. Complexity concepts are explained using Ricardo Wilson-Grau’s ‘Fish Soup Development Story’ – why one plus one does not always equal two, and the implications of this for project management.