That "Adam saw that nothing happened to Eve" is a pretty straight forward explanation of why Adam ate the fruit, but my attempt is in factoring in that he was not deceived into equation and how that might affect the conclusion. For example, Eve saw the fruit was good for food, and desirable for gaining wisdom. Do you think that Adam agreed with her perspective? Or did he know it was "not good" or even evil? Was the tree actually 'not good' or was it only eating of (the fruit of) it that was not good?
IOW, Were they each inherently endowed with the gift of discernment, provided with a choice, and simply chose wrongly? If so, then she eating being deceived evidences some sort of ignorance or something or other, and his choice evidences an apparent rejection of a truth that he 'knew was right,' or at the least an acceptance of a lie that he knew was wrong.
Eve believed a lie, so it follows to assume that she was deceived into choosing the lie, given that scripture is explicit in stating that she was deceived. So I guess I'm wondering what factored into her choice as much as I wonder that Adam was not deceived and what he (choose to) believe as much as why.