From The Propaganda Professor:
I must confess that once upon a time, I was a firm believer in a conspiracy in the assassination of JFK. I was quite skeptical, mind you, of theories implicating the CIA, the FBI, LBJ, or any other notorious set of initials. But I was convinced that Oswald could not have acted alone. Not because I was prone to believe in conspiracy theories in general, but because I just couldn’t get around that seemingly impassable roadblock of the “magic bullet”. Therefore, I concluded that since magic bullets don’t exist, there must have been at least one more shooter. And whenever you have two or more people involved, you have by definition a conspiracy.
I had fallen prey to a type of fallacy that I call the fallacy of single explanations: the rush to a conclusion based on the assumption that just because a particular explanation is the only one you can conceive of under the circumstances, it must be the only explanation possible. You also could call it the fallacy of incomplete data, since these faulty conclusions result from trying to bridge the gap when there is missing information.
The “magic bullet theory”, like many other single explanation fallacies, depends on the presumption that normal conditions apply (when in fact “normal” conditions are largely a myth). But there is one little fact about that fateful day that many people do not consider, a fact involving the seats in the presidential limo ; and it makes all the difference.