Mcluhan didn't know how right he was. How something is conveyed can be more persuasive than what is sought to be conveyed.
Take the evangelical urge for us to tell others of faith in Christ.
Most evangelical church contact is passive. We sit in an auditorium (jokingly called a 'sanctuary' in parts of the USA) and watch and hear others do things to us. The message of the medium is that the experts are active, we are passive.
Then these same experts tells us the very opposite of that which their behaviour teaches: they say, go and tell; but provide no example, no life-experience, no church enaction of the significance of the ordinary parishionner's ability to tell!
Thus, almost no one goes and tells, because this has not been lived in the closest church contact they have.