Why You Should Avoid Explaining a Character's Thoughts

I've been reading The Maze Runner recently, and, although I am really enjoying this action-packed, suspenseful story, I am also reminded that a story is best told when the author shows, rather than explains, the thoughts of the character.

Let me show what I mean, using a passage from The Maze Runner:

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"Who's out there?" he called, his voice shaky and hollow--it sounded as if he were speaking inside an insulated tunnel. 

"Seriously, this is stupid."

He hated to admit to himself just how terrified he was.

In my opinion, the last sentence weakens the effect of the rest of the excerpt. Here's how I feel the language could be improved:

"Seriously, this is stupid."

He clenched his trembling hands and stood rigidly, waiting.

In this remake, we don't get any insight into the character's thoughts, but we can read his terror in his body language. 

Write like you're watching a movie of the action.

Consider the difference between a book and a movie. 

In the book, you get the benefit of the character's thoughts: who he likes, who he doesn't like, whether he's scared, angry, or interested. 

A movie, on the other hand, doesn't interrupt the action with a narrative voice-over: "At this point, Tom feels nervous and scared." No, instead, the movie relies on body language cues to reveal the character's thoughts and feelings: a close-up of Tom's darting eyes, or the bob of his adam's apple as he swallows nervously. We read the cues and deduce Tom's inner state.

Let any revealed thoughts advance the story.

This is not to say that all explanation of a character's thoughts is poor style. Megan Whalen Turner's masterful book The Thief tells the story from the first-person perspective, so it's impossible for the main character/narrator not to provide a little explanation on his thoughts. However, Ms. Turner treads lightly when explaining Eugenides' thoughts and intentions, partially because the reader is not meant to know, until the end, the true identity and purpose of Eugenides. 

Mostly, Eugenides simply reports. When he does reveal his thoughts, they directly aid the plot:

I felt very exposed and worried about who might be watching from above. The last thing I wanted was to be caught hiking across Eddis with the king's magus of Sounis, and we could not have been more visible, five people traipsing through vegetation no higher than our knees.

Use dialogue and body language to flesh out the character.

Just for the sake of experiment, in one of my stories, I deliberately omitted all internal glimpses of any of my characters. Anything a reader learned about a character was judged through that character's body language (which I carefully described) and dialogue (which I crafted with great consideration). 

What happens when you write this way?

"I'm enjoying this," my father commented as I read my story aloud to him. "This is some of the best writing I've seen from you so far."

I'd say the experiment was worth it.