Well I got that there was a boy, a boat and a lot of water, too. But that was about it.
The trailer I saw really didn't show any tiny detail of story - and yes, I was paying attention, thank you. I concentrated on the tiger because that was really all the trailer seemed to focus on. Other than that, all I really got was "this film will have some spectacular 3D scenes in it."
The trailer told me absolutely nothing about the story. The only thing it told me was this was somehow a film I should be really paying attention to. That's what made it worse. It really made the point that this was an "event film," so far from not watching closely - in fact, it convinced me to pay attention. But I still ended up none the wiser.
Sorry if I offended anyone enough that they needed to question my attention span when responding to my post.
My original comment stands, watch it again.
You may have watched teaser trailers which tend to concentrate on parts of the film.
Try this one, it may help
Life of PI