Eve was deceived and followed her senses. She saw with her eyes, and what she saw looked desirable, so she took of the fruit and ate. But Adam wasn't deceived. Adam knowingly disobeyed the commandment of God, and introduced sin to the world. One can't help but wonder what went through Adam's mind when he took the fruit from Eve and took a bite of it. Later that day, Adam would blame not only Eve, but God Himself. (see Adam and Eve Blame Shift) Adam wasn't lacking intelligence. He was perfect, and pure. He had never sinned before. Something compelled him to disobey.
There is a section of Scripture written by James that may shed some light on what happened in the garden thousands of years ago. Human nature hasn't changed since then. “Let no one say when he is tempted, 'I am tempted by God'; for God cannot be tempted by evil, nor does He Himself tempt anyone. But each one is tempted when he is drawn away by his own desires and enticed. Then, when desire has conceived, it gives birth to sin; and sin, when it is full-grown, brings forth death.” (James 1:13-15)
The words “drawn away” imply a strong magnetic-like attraction, a feeling of being powerfully pulled or dragged. This word for desire usually refers to sinful desire, but in Adam's case, sin was not yet in the world. This kind of desire attaches itself to its object. Again, in the Genesis narrative, Adam was certainly attached with desire to Eve. He loved her. She was made by God specifically for Adam, taken from his own body. She was the end of his loneliness, his companion, his best friend, not to mention the only other person in the world!
Returning to the James verses, the word translated enticed means to catch by bait. Eve was the bait the serpent used to involve Adam, powerfully drawing him into the situation like a swirling whirlpool. Adam was hooked and caught. At that decisive moment, his all-consuming affection for Eve overshadowed his good sense. Instantaneously, everything changed, and life for them both would never again be the same.