According to Saldana (The Fundamentals of Qualitative Research), the primary purpose of interviews is while the primary purpose of participant observation

After 20 minutes of waiting outside the baggage claim area for your friend to pick you up, you decide to go inside the airport terminal and phone her. standing a short distance from you is a kind-looking older woman. "would you mind watching my luggage so i can go make a quick phone call? " you ask politely. "i'd be happy to watch it for you," she replies, "my ride is not coming for another half-hour." when you return less than five minutes later, the old lady and your luggage (including your laptop) are gone. this example illustrates one of the problems associated with: ethnocentrism. the "feel good, do good" effect. the rule of reciprocity. an implicit personality theory.