So the subject here is inner dialogue and what it reveals about the lead character in your story. The answer is easy enough and one of my favorites: It reveals as much as you want to reveal. How lovely is that?
There are a lot of variables with this particular subject. The question really is how much do you want to reveal? If the main character is a man of mystery as it were, you might want to reveal amazingly little. On the other hand, the wiser way to handle that might be to have the character in question seen and observed by someone else, thus avoiding any internal monologues. Example given: It was Watson who narrated the Sherlock Holmes stories. For that reason we only saw as much of Holmes’ mind as Watson was privy to.
I like what characters have to say to themselves. I think it reveals a good deal about them and that’s one of the things I like about books over movies. To be fair, there’s normally a lot I prefer about books to movies, but that’s one of the big ones for me.
I did a story called SMILE NO MORE in which the main heavy is a dead clown. Okay, he’s rather active for a dead clown, and he’s a bit of a basket case, but I also decided to reflect that in how I approached the novel. Certain sections were done in the first person, from two different time frames within the same character’s mind. There’s a lot of internal dialogue. The rest of the novel is told third person, limited omniscience. There’s even more internal dialogue, but it’s from the perspective of the people who are dealing with the aforementioned dead, insane clown. You may rest assured that how they see the clown is a bit different than how he sees himself. He is, of necessity, the hero of his own story. His motives, his actions, his reactions all make perfect sense to him, and as a result of how the story is written, I managed to pull off a very important part of the tale: I managed to evoke a fairly strong sense of sympathy for an exceedingly unsympathetic character. More than one reader and reviewer both complimented me and chastised me for making them like a man who is very much a monster. I take that as a point of pride. It means I managed to pull off what I was trying to get across.
The thing is that I think if a writer handles the internal monologue(s) properly, you can learn a lot not only about the main character(s) but also about how others see them. In a few cases in SMILE NO MORE the characters that our—I hesitate to call him a “hero”—encounters are genuinely not nice people. They sort of deserve what they get. Okay, maybe not to the level that is dealt out, but they sort of deserve justice for the things they are doing or have done. A good deal of what makes them reprehensible is only seen through their internal monologues. It was a challenge to make them seem human and a challenge to make Rufo the Clown seem like a nice guy. Their own thoughts are what made that possible and I’m genuinely not sure if the story could be told as easily in a movie format for that exact reason.
That’s just one example, of course, but it works as an example of why I think the internal voices of characters are significant to driving a story.
Our Hero: Rufo The Clown