If you say, "Evelyn had a broken leg," readers can’t feel anything, but if you describe a bare bone sticking through pale skin or describe the way she hobbles on crutches, they vicariously experience Evelyn's pain.
This is especially important in dealing with the emotional state. Don’t just say a person is depressed; readers need to see the person acting in a depressed mood. It’s the adage that actions speak louder than words—especially telling words. When done well, showing reveals character and enables readers to feel they are participants in the events.
Suppose I relate an incident when I arrived late for my English class. Before I write, however, I need to decide what information and emotion I want to convey to my readers. Notice the differences in the three examples below:
1. I walked into Miss Anderson’s classroom five minutes late. (This presents information without emotions.)
2. I raced into Miss Anderson’s classroom, desperately hoping she wouldn’t see that I was late. (Readers can visualize this.)
3. I sneaked into Miss Anderson’s classroom as the clock ticked again. I cringed to realize that I was five minutes late. (This enables readers to feel my emotions.)
No matter how small the action, describe and don’t merely inform. The example above shows how much life you can add to a single sentence by the use of a few words.
You could make the illustration even stronger: I sneaked into Miss Anderson’s classroom, desperately hoping she wouldn’t see that I was five minutes late. My pulse raced, as I tiptoed to my desk. Just then my book crashed to the floor and heads turned toward me. Miss Anderson's dark eyes glared.
Ask yourself: When I show, what do I want readers to feel?