Well, the word itself is an allusion to how a supporting tentpole holds up the fabric of the tent and/or to how a single must-see act, can draw the crowd for and support smaller acts within the circus.
If you don’t have a tall and strong tentpole, you don’t have a big top tent that you can perform under. And if your circus doesn’t have a tentpole act, you won’t have a large enough crowd to make the whole thing profitable.
In the movie business, a Tentpole Movie is a high-concept, sure-fire hit that typically appeals to a four quadrant audience (men, women, boys and girls) and contains universal and culturally relevant themes. In other words, a film with enough story-power and star-power to ensure profits capable of supporting the studio financially.
In my world, a Tentpole is similar to traditional advertising’s Big Idea is an exciting and unusual Branding Concept that has:
Universal appeal (within our targeted audience),
A relevant theme, and
The ability to keep an audience tuned-in to hear the rest of the story.
And in my not-so-humble opinion, running a branding campaign without a tentpole is about as smart as pissing on an electric fence.
Can you run a successful branding campaign without a tentpole?
Maybe about the same way you might be able to piss on an electric fence without getting zapped. Point is: why would you want to try?