Introspection is an intentional implanting of thought into a character's mind to reveal his response to an event. It can give a clue to what course of action he would take. The lack of introspection leaves the reader blind, having no way of understanding how an event affects a character. Physical action may reveal a response, but what he thinks while an event is happening doesn't give the reader any clue. Mental and physical responses are two different reactions. Mental response often comes first. Without introspection, the reader could wonder why a character punches another because the character's rationale behind it is hidden.

Example without introspection: The Magistrate stood and pointed accusingly at Catherine Morgan. "She's a witch!" The other villagers gasped in shock, and the women exchanged whispers. The Magistrate ordered silence. Catherine stared back at her accuser, unmoved as he continued: "She is responsible for bringing the plague into this village. Since the death of her husband, she has become vengeful, and she will not stop until all of us are dead!" Catherine swept her eyes over the crowd, who had made up their minds on what to do with her.

The writer chose to omit the thoughts of the woman accused in a witch trial. While we know that she is unmoved at the baseless accusations, her immediate thought about the situation is lost. The reader then has no idea what she will do next. Will she burn at the stake? Will she escape? Will she defend herself at the trial? If this scene continues with physical description without introspection, the dramatic element will be lost.

Example with introspection: The Magistrate stood and pointed accusingly at Catherine Morgan. She's a witch!" The other villagers gasped in shock, and the women exchanged whispers. The Magistrate ordered silence. Catherine stared back at her accuser, unmoved. Fools, she thought. They are the ones who should burn. She didn't believe that her husband died from a hunting accident. The Magistrate connived with the hunting party to kill her husband, who had long expressed a desire to leave the village and live independently. She won't allow them to kill her too. "She is responsible for bringing the plague into this village," continued the Magistrate, "and since the death of her husband, she has become vengeful, and she will not stop until all of us are dead!" Catherine swept her eyes over the crowd, who had made up their minds on what to do with her. I shall burn this village to the ground!

Introspection can be optional. The writer must insert this technique at the right moment, where he thinks a character's thought process is essential to convey more drama. In the past, stories were more introspective as writers prefer delving more into characters' thoughts. But practices in the writing craft conform to the changing taste of publishers and readers. Nowadays, introspection must be used sparingly or balance character thoughts with action. Too much introspection could interfere with the rhythm of the action and vice versa.