A clinically insane person is detectable as such. Talking to themselves (or perhaps voices only they can hear) is one prominent sign.

When I see a homeless person talking to themselves I have a strong emotional reaction that empirically makes me optimize to ignore them. I have a "talks to themselves" detector. So do others.

In principle there is nothing insane about talking to yourself. We do it all the time in our thoughts, when writing, or when recording a video. Doing these things is easy. But somehow it feels wrong to just talk to yourself out loud.

Because other people have the insanity detector $I$ hooked up to a strongly negative reaction, it makes sense that you'd have an a program $D$ in your head that optimizes towards not triggering $I$.

Insane people are unpredictable. Unpredictable implies dangerous. They might try to cut open your skull because they believe this will free your mind. They might really want the best for you but then their world model is so messed up that their actions have the opposite effect (of cause there are many different kinds of insanities).

In the ancestral environment insane people were detected and often killed I retrodict, creating a selection pressure for $D$.

Talking out loud to yourself about your devious plan to dethrone the alpha male is bad even when you aren't insane.

But for $D$ to exist and for us to also constantly talk in our mind implies that talking to yourself must be really useful. Why else would we do it most of our waking hours?

But here is the thing: Talking out loud is even better. There is something about forcing your thoughts into language that reveals gaps in your understanding. It's the inability to turn a conceptual thought into language, combined with a feeling of confusion, that tells you that there is something more to figure out.

Say out loud what you want you are just about to write down. By noticing how you feel about what you said, you can notice if you can do better. And iterating in spoken language is much faster than in text.

When I tell somebody, "I am recording a video" this is a sufficient explanation for me not being insane, even though I'm talking to myself. I find it much harder to say out loud what I am just about to write. I hope this text can provide a similar explanation that I can direct people towards. Hopefully the mere possibility will make $D$ less active.