This also supports that: if person A has the expectation "they'll interrupt/reply once they understand" and B has the expectation "let the speaker finish", this leads to A rambling. (A has no indication that things were understood).
I think in a lot of situations there needs to be one of the parties that steers the conversation a bit - interrupt themselves or the other party if they're going on a tangent. It takes some time and practice but it will pay off in the end.
