Culture eats strategy for breakfast.
The real story
The Drucker Institute at Claremont Graduate University states Drucker never said or wrote this. Quote Investigator's investigation (May 2017) found no occurrence in Drucker's works and traced the saying to early-2000s business consulting circles, with Mark Fields (Ford) as the most prominent early user. The linkage to Drucker is "not well supported" and appears to be a case of posthumous folk attribution. See: https://quoteinvestigator.com/2017/05/23/culture-eats/
Context
This pithy phrase is ubiquitous in management circles and almost universally attributed to Drucker, yet no researcher has found it in any of his books, articles, or recorded speeches. The earliest documented use dates to a September 2000 trade journal article (PIMA's North American Papermaker) by consultants Bill Moore and Jerry Rose. Mark Fields, then a Ford Motor Company executive, popularised the exact wording "Culture eats strategy for breakfast" inside Ford around 2006. Drucker's name became attached only around 2011, years after his 2005 death.