A psychiatrist/journalist/some dude blogged that he ran a test for fun about inner voice - or better yet, the lack of it and found out that majority of people don't even develop the so-called inner voice. These "NPCs" just live out their lives, reacting and thinking in a way that is handed to them, while people with the gift or capability to mentally yap to themselves could "think on their own".
https://www.psychologytoday.com/us/blog/pristine-inner-experience/201110/not-everyone-conducts-inner-speech>If not multiple experiences, what are the frequently occurring phenomena of pristine experience? Chris Heavey and I gave random beepers to a stratified random sample of 30 students from a large urban university and interviewed them about the characteristics of their randomly selected pristine experiences. Five main characteristics emerged, each occurring in about a quarter of all samples (many samples had more than one characteristic). Three of those five characteristics may not surprise you: inner speech occurred in about a quarter of all samples; inner seeing occurred in about a quarter of all samples; and feelings occurred in about a quarter of all samples. The other two phenomena occurred just as frequently but are not so well known.>Consider inner speech. Subject experienced themselves as innerly talking to themselves in 26% of all samples, but there were large individual differences: some subjects never experienced inner speech; other subjects experienced inner speech in as many as 75% of their samples. The median percentage across subjects was 20%.>As a result of this study and others we have conducted, I'm confident that inner speech is a robust phenomenon-if you use a proper method, there's little doubt about whether or not inner speech is occurring at any given moment. And I'm confident about the individual differences-some people talk to themselves a lot, some never, some occasionally. 
