“The most efficient and effective method of conveying information to and within a development team is face-to-face conversation.” —The Agile Manifesto
This principle was needed in 2001, when the Agile Manifesto was written, because most employees worked in cubicles, and many projects were managed as tasks and handoffs from one team to another. Waterfall-style project management methodologies had a high failure rate, which led a growing number of organizations to shift to scrum, Kanban, and other agile methodologies.