Diverse actuation systems are an attempt to cope with unknown unknowns that may lead to common cause failure in the design of I&C safety systems in nuclear power plants. The diverse systems protect against postulated common cause failures internal to I&C safety system design, but are these really the most likely hazard? The intent of this paper is not to fully answer that question, but to begin a discussion of whether diverse actuation systems are the best way to address the unknown unknowns. Appendix 1 of this paper examines 19 severe accidents to identify the causes for safety system failures or late action that contributed to the events that resulted in significant core damage, as well as he contributions of diverse functions where such features played a role in the accidents. The paper also explores: • The role modern diverse systems might have played had they existed during the 19 events, and • Potential alternatives to diverse actuation systems.