While the short answer is no, a tour guide does not need to know "everything," a high-quality guide must possess a deep and structured mastery of their specific subject area and be an expert in "finding out." A guide’s value lies less in being a walking encyclopedia and more in their ability to tell a compelling story, manage logistics, and handle the unexpected. Professional guides are trained to admit when they don't know a specific, obscure fact rather than making up an answer, which preserves their credibility. However, they are expected to have "foundational expertise" that covers the historical, cultural, and technical aspects of the tour. The best guides also possess situational awareness—knowing where the nearest restroom is, which restaurants are safe, and how to navigate local customs—which is often more practical than knowing a specific date from 400 years ago. Ultimately, the "must-know" for a guide is how to facilitate an engaging experience while maintaining the safety and curiosity of their group, using their knowledge as a tool rather than a performance of pure memorization.