Here is one plain message. Tap through the media below and watch the same facts get re-made into four completely different things. Notice how each form changes what can be said, and what you walk away with.
The messageThe tap water in our town is clean, safe, and free to drink.
Tap a medium to see it.
Seen: 0 of 4
Same message, four different things. The billboard could carry a claim but no proof. The video had to earn attention before it could say anything. The long read could argue and evidence its case. The podcast ran on a person's voice, not on facts at all. The form decided what could be said, and what you took away.
That is "the medium is the message" (McLuhan, 1964): a medium's deepest effect is not the content it carries but how its form reshapes attention and meaning. The rule follows directly: build creative for a medium's grain, do not lift one execution across all of them, and never assume reach alone will carry a message the form cannot hold.