The definition of the insist on
phrasal verb told us that it means to keep doing something, even if it annoys other people, or people think it is not good for you.
In contrast the definition of the just insist
verb is to say firmly or demand forcefully, especially when others disagree with or oppose what you say.
I'd like to clarify the difference between them. As far as I understood insist on
assumes that we're already doing something, but just insist
told us that we're just saing firmly about our intention to do something. So, in the sentences with insist:
I don't know why you insist on talking about it.
The listener is already talking about that "it".
I don't know why you insist to talk about it.
The listener's just saying firmly to talk about it, but not talking yet.
Is it correct?