The customer interview is the most basic technique I'll discuss in this book. I wish I didn't need to include it because I'd like to be able to take it for granted that product managers already know how to do this well and do it frequently.
However, the reality is that this is often not the case. Or, if customer interviews are happening, the product manager is not present, so the learnings are not understood viscerally or taken as seriously as they need to be (see Discovery Principle #10 on shared learning).
But no question, this is one of the most powerful and important skills for any product manager and very often the source or inspiration for many breakthrough product ideas. Later, when we discuss techniques for testing your product ideas qualitatively, these skills will be a prerequisite.
There are many forms of customer interviews, so this is not really a single technique. Some are informal and some are more formal. Some have a user research methodology behind them (one of my favorites is the contextual inquiry), and others are more about just getting out of the building and learning what you don't know.
But in every user or customer interaction, we always have the opportunity to learn some valuable insights. Here's what I'm always trying to understand: