By looking deeply into human lives, 1) we ensure we're seeing the full story, 2) we validate that the experience is real, and 3) we capture highly specific patterns that offer instructive guide for design.
Despite the emergence of new data collection tools, the ethnographic interview is still the most sophisticated tool for exploring intimate details of personal life. When done well, it establishes the trust and vantage point necessary for participants to reveal behaviors and beliefs often veiled by the force of habit and routine.
A great intellect won't get you there alone, you also need empathy.