What is our best understanding behind why JFK was assassinated?

by from_dust

After looking through the FAQ i wasnt able to find anything on this topic. Obviously there has been an abundance of speculation, conjecture and conspiracy theories on this topic, so much so that, its become difficult to separate the truth from the facts. I've seen a few documentaries on the matter and the story is so well entrenched in American history, that it confounds me that i still dont really understand what was the motive behind it? is the official record on this matter clear or is there much we still dont know? What the hell happened?

from_dust

EDIT: clearly i meant "separate truth from fiction"