Greetings in that Divine and Most Precious Name of Our Lord and Savior Jesus Christ!
It's really stupid if you think about it, but Adam and Eve were very naive.
Personally I never thought Adam and Eve were naive at all, I thought they ALWAYS knew exactly what they were doing, perhaps they weren't aware of the gravity of their mistakes. I'm not quite sure what was Eve's motivation for giving into the temptation of the Serpent, I'm not a woman so I can't really understand the depth of that moment. However, as a man, I've always had my own insight about why Adam followed her sin and also ate. He said she deceived him, he was lying. People are not that stupid, we just like to pretend we are so garner sympathy or at least a free ride out of a given situation. No, I think Adam knew EXACTLY what he was doing, I think that Adam fully understand that Man was created in the Image of God, that Man was the archetype for the coming of the Word Incarnate. If Adam knew this, he also understood that God didn't have intentions of immediate destruction of mankind. Adam was calling God's bluff. God didn't want to destroy Adam, and He didn't. God didn't want to destroy Cain either, even though Cain committed the worst of human crimes which is cold blooded murder, and yet God forgave him too! Clearly Adam and Cain knew something about God we have forgotten, His Love, Compassion, and Forgiveness. So I think that after Eve ate of the fruit, that Adam was afraid for her, more particularly, he was afraid of losing her. What man hasn't made silly and self-defeating sacrifices for the sake of the love of a woman? How many men have beat their heads against that stone wall? So I always felt that Adam knew God wouldn't destroy MAN, but he wasn't so sure about what God would do with women who were created after, so Adam at the fruit to be complicit with Eve's guilt, to test and challenge God. Sort of like a cosmic and existential, "Ah ha! Gotcha God! See if you really want to destroy me.." Its the same way our own children play with our emotions and push our buttons and test our tempers, they KNOW we aren't going to seriously hurt them no matter how angry we get, no matter how justified it may seem..
God could have easily done that, and created an entirely different person to become Jesus Christ in the Incarnation, but for whatever reasons we can't understand God chose Adam, and from Adam's descendants came Our Lady and the Savior in the Flesh. God chose Adam's flesh, and I think Adam knew
this. So Adam ate the fruit I think fully aware of the potential punishment, but was hoping God wouldn't do it for the sake of His plans for Adam. Adam loved Eve enough to sacrifice himself. Perhaps Adam thought that either (a) if God has to kill Eve for this crime, then He will have to kill me too which it seems God didn't want to do or (b) that Adam loved Eve enough to be willing to lose his own life to be with her in Hell. Its a bit campy and romantic, true, but its how I feel about that particular story.