Nuance gives interactions depth. The change of tone, the raised eyebrow, the subtle shift in posture—all of them indicate attitude and feeling. It's what makes story interesting, movies gripping, and real life easier to interpret. Without nuance, face to face interactions lack a certain emotion that we depend on to understand what's really going on. Even stranger to stranger interaction has subtle nuance, whether discomfort, disinterest, or delight.
Nuance differs from person to person, but some things are universal. Do you look up to the sun with your eyes closed when you go outside? Are you constantly picking at things with your fingers? Do you lean in when you're listening, cross your arms when you're upset, yawn when you're bored? Subtleties help us process interactions—without them we can't tell what the other person is thinking, unless they come straight out and say it. Was he leaning out because he wasn't listening? Why didn't she nod? What is all the yawning about?
In the same way, writing nuance into your story clues your readers into what's really going on, and triggers the imagination to help tell the story and fill in the tiny missing pieces. Without nuance tips, we won't know the tone of the story.
How do you write nuance into a story?
#) Understand what nuance is. You can't write it unless you understand it. Fortunately, it's an easy thing to learn. Eighty-five percent of social interactions that you witness are full of nuance—and once you start looking for it, it's everywhere.
#) Read for it. Find popular writers (both current and classic) and read their work. Do they use nuance well? Poorly? At all?
#) Practice. This is the dead horse that I'll flog forever, when it comes to writing. The only way to get better is to practice, even when you don't feel like it, even when you have nothing to say. Look at the objects on your desk and write a story about them having a conversation. If your desk is empty use your shoes. If you're not wearing shoes, write it about the wall and the paint. If you write in a gazebo, maybe you're in a public park and there will be people walking by... You get the picture.
Nuance is invaluable to writers. Perfect the art.