There is an awful lot of talk about "original sin,"  but no one seems to be clear
on exactly what the original sin was. I've heard all sorts of conjecture. Let's
look at some of the more common theories.

Because our society has become so repressed, most people latch on to the idea
that the original sin has something to do with nakedness or fornication. There
is no real biblical data to support this assessment. Adam & Eve only realized
they were naked after they had sinned.

Next people say they were trying to "be like god." This is also an incorrect
theory. According to the book, Adam was created by god in god's own image.
(Well, technically Adam was created in "their" image. But no one is really sure
who in the hell god is talking to when he says that, so it's usually brushed over
quickly.) And Eve was created by god in Adam's image. They were already like
god...

The last theory I commonly hear is that it was learning the knowledge of good
& evil... (i.e. right & wrong) that marks the original sin. Again, this can not be
the case based on the story itself. God says don't eat of this tree. He has
established a pretense of right & wrong from that moment forward. To say that
this knowledge resulted from the sin would be to ignore the rules of cause and
effect.

Adam & Eve had to already possess "freewill" at this point in order to be
disobedient; therefore, we can surmise that disobedience itself was the original
sin.

Here's the interesting part. God tells Adam & Eve not to eat from the tree or he
will kill them. However, according to the story, they have no concept of right or
wrong prior to eating the apple. Therefore, they had no way of knowing that
they were committing a sin by their actions. They may have been given the
tools to make a decision, but they could not possibly grasp the consequences.
Did they even understand the concept of death? Not having defied god prior to
this event, they had no experience to base their decision on. With out a
adequately defined set of parameters in which to operate, they were clearly set
up to fail. (Interestingly enough, when they do disobey god, he doesn't kill
them. So it turns out to be the first in a long line of idle threats and half truths.)

Furthermore, because god, by definition, is all knowing, you could easily argue
that they were destined to fail. (My thoughts on the Myth of free will in the
christian paradigm explain this a bit more thoroughly.)