I once read somewhere that teaching only happens when someone learns something.
So just because you spent an our lecturing doesn't mean you necessarily taught anything, unless someone actually understood what you were trying to say.
I find that the same holds true for any type of communication. Communication only happens when the listener actually understands what you are meaning to say. And it turns out that this is actually pretty hard. I've been thru countless meetings where people came out thinking very different things, with each one convinced that he has the right interpretation of what went on and what was said.
There are many reasons why this happens, but here's a simple analogy: If you are transmitting something on radio, and your equipment works, you will always be sending out what you think to be a clear signal.
But on the receiving end, sometimes the radio is not tuned properly. Or the listener is in a noisy environment, or maybe he is simply not interested and just turned on the radio as background noise. In any one of these cases your crystal clear message turn into garbled nonsense.
The point is that communication is a two-way process. Listening, absorbing, and understanding is as much part of it as the speaking and presenting.
So let's say it again: Communication only happens when someone gets your intended meaning - otherwise it is just noise.