“A Lean thinker is interested in and in a way even welcomes (if not joyfully) the appearance of interruptions, anomalies, and problems in his or her process as opportunities to understand and eliminate sources of variation and disruption. This root cause orientation to corrective action is a powerful engine in driving continuous, lasting improvement.” 

Creating a Lean Culture, 3rd Edition  by David Mann (CRC Press, 2015), p. 225.