I learned that the laws of physics do not apply to huge floating mountains.
I learned that infectious diseases do not affect either the human or navi populations.
I learned that a stone age lifestyle is a preferential one.
I learned the navi do not need dental or medical care at any point in their lives.
I learned that the navi don't need to be worried about volcanoes, climactic changes, asteroids, or other calamities that are capable of destroying the majority of life on Pandora, let alone their spirit trees.
I learned that the best way to commit interplanetary genocide is to still use circa Vietnam War technology, with foot soldiers and helicopters, instead of biological, chemical, or nuclear weapons... or even long range rockets... or orbital bombardment... or blankets laden with small pox.
I learned a few tribes of navi will have the power to stop the humans from doing the same thing on the other side of the planet.
I learned that if you expect to be attacked by swarms of pissed off aliens, the best way to save yourselves is to go into close combat with them and take heavy casualties rather than say... oh... evacuating.