When Pandora was first opened, Yi was tempted to burn down that giant tree on the horizon.
But later, due to too many people rushing in wanting to complete the [Ultimate Challenge], and the Tree of Life was almost unanimously believed to have an [Ultimate Challenge], he had to abandon this wild idea.
However, in the player forum, there have always been quite a number of players declaring boldly that they want to "set fire to the World Tree".
The main reason why no one had actually done it before today was not for lack of desire, but inability.
—This is not just burning an ordinary tree.
This is an astonishingly huge tree, tall enough to cross the cloud layers and so thick that it would take six native tribes to surround the trunk!
Without enough, or strong enough kindling, it would be impossible to ignite.
Not to mention the six surrounding Na'vi tribes—they surely wouldn't sit idle and watch their sacred tree be burned by a group of aliens.