The Planning Fallacy principle, a prominent account of project behavior and particularly the causes of cost overruns and benefit shortfalls, stems from the belief that bias outweighs error. Its very popularity begs for an inquiry on its theoretical appeal and whether it remains a viable argument to explain cost overrun and benefit shortfall behavior. This chapter argues that the Planning Fallacy is in danger of danger of being debunked, suggesting that while its rise can be attributed to an impulsion to theorize, its subsequent fall may be due to a companion compulsion to theorize. The chapter focuses on three questions: Is the Planning Fallacy principle a theory anyway and, if yes, is the theory complete? Is the theory too narrow in scope or does it cater to complexity and uncertainty? Will it lose support from the scientific community? The chapter demonstrates that the fall may be due to the incomplete nature of the theory and its limited scope. The chapter contends that the popular appeal of the Planning Fallacy has vastly overstepped its ultimate viability and suggests that the Planning Fallacy principle is itself a form of Planning Fallacy as it overestimates its own theoretical power.