The Lean Startup has a lot to answer for: a generation of project, startup, and business leaders think they can get the answers they need by running ad experiments, building fake doors, and running A/B tests. Perhaps it's introversion; perhaps it's an over-belief in the power of data. What it certainly leads to is a lack of insight into who your users really are and what their lives look like.
The most important question when you're building a new product or service is why. It's not enough to know that people seem interested in the thing you want to build. Why are they interested? What are the stories behind their frustrations or their curiosity? If you're trying to improve an existing process, why do they do it in the way they do it right now? Why do they need something better?
The trap that most people fall into is to intellectualize an answer to this question. Perhaps they think they're smart and can just make up the answer using a combination of creativity and inference. Or perhaps they've constructed an artificial persona from a few data points - which, in reality, is the exact same thing as making up the answer from creativity and inference. In both cases, any surprising insights you learn about your users actually come from your imagination, rather than reality. But you might think they're real, and use them as the basis of a strategy you have no idea is misinformed.
Most people, particularly when they're starting out, don't have the kinds of participant numbers that would make quantitative research statistically significant. But even with those numbers, surveys and experiments rarely get to the why.
There's no alternative to getting out and talking to people: understanding their lives, and learning the stories behind their work. It's about undertaking a project with humility and understanding that you probably don't know all the answers. It's also about finding the surprising insights that nobody else knows - something you can only figure out by talking to people.
Qualitative research is incredibly powerful. For introverts, it can be uncomfortable - but the results outweigh a little discomfort. Making your project truly human-centered by always going back to the user can help you avoid building the wrong thing, and create genuine innovations that really help people in a way that statistical research (or worse, just building without any understanding) simply can't.