[E]very year, I tell my students that marketing is the only function with the organization that is expressly designed to sit at the intersection where business meets people. Real people. And the problem with real people is that they don't see the world the same way a businessperson does. they don't speak the language of bullet points; they don't organize the world into flowcharts and frameworks. People, real people, view the world more organically. They are idiosyncratic. They are unpredictable. They are beautifully disorganized.
Youngme Moon in Different (p. xvii) discussing the how people differ from our ideas of them.
As a product manager, I strongly disagree that marketing is the only function in a company where the business meets people (I'm pretty sure most of our customer service department would, too).
Nevertheless, I love Moon's description of real people. It reminded me of something Peter Morville wrote about the ambiguity inherent in communication.
Our ways of thinking about the people for whom we're designing–segments, personas, etc.—are in many ways inaccurate. They can also be useful is used thoughtfully.
Nothing replaces spending time with people face-to-face. I recently did some testing of some changes we were making to a key part of our product at work. Whether I went out to see our customers or brought them into the office, I invited other people from around the company to take part in the testing. This was much more effective than any report I could have written or video I could have shown. People came back from the excursions knowing what we needed to change and why. I didn't have to say a thing.