Satan

Satan said to Eve she would know good and bad if she ate from the tree.  Before she looked longingly at the tree there was only one bad thing she could do, but she didn't know that yet because she didn't take from the tree yet.  Then when she took it everything went bad.  So Satan tricked her it was either nothing or everything.  Now that she had done the bad thing Adam knew it and he went with her.  It was already done.