Genesis 3:5

"'For God knows that when you eat of it your eyes will be opened, and you will be like God, knowing good and evil.'" Genesis 3:5

Here the serpent is tempting the woman with the promise of power and knowledge.  Just think, to be like God, in all his splendor and glory.  Who wouldn't want that?  And the knowledge of everything...The first temptation was a big one.  One bite had a lot of power.  The fall makes so much more sense now.