Lessons from a hazard and operability review (HAZOP) can be vital to safe operations throughout the life of any plant . These lessons can come at a very high price. But, as the popular Mercedes Benz ad goes, “there are some secrets too valuable not to share,” In this paper incidents are documented at different phases of a type of plant's development. The phases of development include design/construction, initial startup, and normal operation. The type of plant of concern is the sulfur recovery unit in a refinery. How the finds impacted each project are detailed with resolutions and insights of the importance of performing a HAZOP with individuals intimately familar with the plant, with adequate preparation (meaning having available up-to-date and complete documentation), and following through in a systematic and thorough fashion. Also the importance of HAZOP updates throughout the plant's life are emphasized.