The document discusses the history and evolution of the "pets vs cattle" metaphor for describing how servers are managed. Originally, servers were treated like pets that were individually cared for, but in modern cloud computing they are treated like cattle in a herd that can be replaced without individual attention when one goes down. This shift reflects how infrastructure has become automated, standardized and able to dynamically scale out on demand. The metaphor helped explain why cloud computing was different from traditional IT and how failures could be handled without impact.