The long pole obscures the other poles.

While it's the long pole it obscures what the other poles are--you literally can't see them, because the tent, held up the long pole, doesn't rest on them.

There could be a lot of other poles that are almost as tall, or most way shorter... you don't really know until the long pole is gone.

While the long pole is there, it will look all-important.

But once it's gone you can see that there are other poles that are now the longest.