Here's an example from a recent strategic planning session in my company.
On several occasions during the planning session, I said "I've already given you that", or "we agreed on that before".
However, if we really were communicating, then there wouldn't still be an issue. Clearly, something was getting in the way of true communication.
What Can Cause This?
One of the issues was "bandwidth". If someone feels so overwhelmed that they can't take in anything more, then what would have been signal turns out to be noise. Another way to say that is even a reasonable request can seem unreasonable if the person is overwhelmed and doesn't feel like they have the resources to accomplish what they need.
A related issue is understanding, but not agreeing. In other words, we can talk about an issue ... but until someone says "yes" there isn't agreement. For example, in a car dealership there's a difference between saying "I really liked that car", or even "I really want to buy that car", versus "yes, I will buy this car."
The same dynamic plays out in a business meeting, and the stakes are often higher.