"The woman saw that the tree was beautiful, that its fruit was good to eat, and that it would make her wise. So she took some of it's fruit and ate it. She also gave some of the fruit to her husband, and he ate it.
Then, it was as if their eyes were opened. They realised they were naked, so they sewed fig leaves together and made something to cover themselves."
I think this demonstrates pretty typical human behaviour. We are never content with what we have, we always want more. I suppose I'm a pretty good example of this, I have lots of books, but if I go into a bookshop I can't help but want to buy more of them, despite the fact I have a good couple hundred books I havn't read.
The point is though, she wanted something she didn't have. She took it. And in the process she lost a gift she had which was precious. Her innocence.