In the book of Genesis, the serpent "beguiles" Eve.  Tempts her with a thing she isn't supposed to do.  Temptation is always about something we aren't supposed to do.  Something forbidden by society, parents, or God.

Eve is about to do something that seems like a small thing--eat a piece of fruit--but it isn't small, it is huge.  It really doesn't have anything to do with fruit.  It has to do with obedience.  God could have just as easily said, "Don't jump up and down."  What he forbade wasn't the issue.  It was simply that He said "Don't do it."  So she did.  And so did Adam.

Gen.3: 6 "And when the woman saw that the tree was good for food, and that it was pleasant to the eyes, and a tree to be desired to make one wise, she took of the fruit thereof, and did eat, and gave also unto her husband with her; and he did eat."

She saw.  It was pretty.  It would make her wise--the serpent said so.  She took the fruit.  She ate it.  She gave it to Adam.  He ate it too.

When I teach young women who have children, I tell them that when you have a child, you will spend the rest of your life trying to teach them to "do the right" thing.  You will never ever, ever, have to teach them to do the wrong thing, they do that all by themselves.  We are pre-programed to do wrong.  We are born self-centered, selfish, greedy, thoughtless, unkind, etc., etc., etc... and until we have guidance by a moral code, we don't think in terms of others at all.

But it takes more than a moral code.  It takes an internal revamping that we are not capable of doing for ourselves.  We have to have an inside transaction that causes an internal change.  We have to have the Holy Spirit.  "Christ in you, the hope of glory." Colossians 1:27 God comes in, and changes you from the inside out.  Moral codes change you from the outside in.