First-hand, hight resolution user research
A good (usable) design starts with taking a good look at how people use a product. When talking about field studies, all too often it is seen as just a means to define the product in terms of functionality. Market Intelligence goes out and observe people to see what products they might need or want. But field studies are also the natural starting point for designing a user-centered product. Designers should get first hand, high-resolution (including those seemingly meaningless details) information about how people use their products.

Designers don't get out there
However, most designers or product managers I talk to don't get the chance to do this. "Listen mate, we hire you to design, not to walk around town." When she wanted to take a look in the shops to see how his products were positioned, and what competitors there were on the shelves, a former class mate of mine, who became a product manager at a big consumer electronics company was told that: "You can look in stores all you want over the weekend. Work takes place in the office."

The Sony Streetstyle Headphones
To illustrate what a keen eye for product use can lead to, let's look at the story of the first Sony Streetstyle Headphones, as documented in the book Digital Dreams, The Work of the Sony Design Center, by Paul Kunkel.

Kazuo Ichikawa began to focus on a newer, more casual style of headphone that would fit behind the neck rather than over the head or directly in the ear. [...] His inspiration came from the way people use conventional headphones in the street (allowing them to drop behind the neck), how people wear baseball caps (often with the visor pointing backwards), and the apparatus that folk-singer Bob Dylan used to support his harmonica while performing in concert.
"A critical issue when designing headphones is to make them fit properly," says Mr. Ichikawa. "Yet there is a huge difference from one person to another in the distance from one ear, over the top of the head to the other ear. When you factor in hair styles and the possibility of a cap or hat, you realize that the traditional headphone is no good."

Just tell me how you would get inspiration like that while sitting at your desk.