Call me crazy, but I think that an internal monologue is a "you" instance running beside your main instance.<p>The "you" is because "you" are a lot of smaller stuff instances of things running along in your brain.<p>Probably it's common to develop this multiple "yous" and kept them happily running (may be with therapy some get to "shutdown" or "suspend" some "evil" "you" they have running and messing everything).<p>But some people don't need several instances of themselves, and they just run one "you" thing. Hence, no internal monologue.