If the agile Prime Directive is embrace change, a close second is embrace communication and feedback. The manifesto and principles, and agile methods have a theme of working to increase communication, especially face-to-face conversation. This is illustrated in practices such as the daily Scrum meeting and XP's requirement to have onsite customers sitting full-time in the common project room.
Agile methods are adaptive, requiring feedback to guide direction. Beyond just conversation, they seek out early and frequent feedback through early testing, early demos, and much more.