it seemed so harmless

The Lord God gave the man this order: You are free to eat from any of the trees of the garden except the tree of knowledge of good and evil. From that tree you shall not eat; when you eat from it you shall die.  (Gen. 2,16)

But the snake said to the woman: “You certainly will not die!

It seemed so harmless. Just one individual eating good fruit from a good tree. There was no reason not to, other than that God said not to do so. Besides, God didn't say it to Eve, he only said it to Adam.

Indeed, they ate of the fruit and experienced no harmful consequence. In fact it was kind of good: Then the eyes of both of them were opened. Perhaps it was all a misunderstanding.

So what's it to you that Eve wants to eat from that tree. She's not doing anything to you. It's between her and God.