A low success rate of improvement projects is one of the causes of the discontinuity of lean six sigma (LSS) initiatives in companies. It is essential to identify and evaluate the reasons why LSS improvement projects fail in order to enable LSS, Lean, and six sigma sustainability. This article presents the findings from a global survey conducted with 201 LSS experts around the world in both the service and manufacturing sectors. The results of this article point out the significant failure rates for LSS projects and alert that projects had higher termination rates in the measure and analyze phases define, measure, analyze, improve, and control (DMAIC). Failures occur primarily at the corporate level. The main causes of project failures identified were the lack of commitment by top management, resistance to change, inadequate rewards and recognition mechanisms, inconsistent monitoring and control of the projects, and poor communication. This article shows that there are some minor differences in terms of ranking of these factors between the manufacturing and service sectors, but there is a significant difference in terms of continent and belt level (master black belts, black belts, and green belts).