In any case, a rebellion did happen, Satan and his angels were cast out of Heaven, and they are warring against God's rule in the created order. The origin of Satan's sin may be an interesting topic, but there is simply no evidence for us to go on other than the facts listed above.
That being the case, we will look at the origins of sin among humanity. The single most important fact that we must consider in this context is that our sin originates with Satan. As such, all sin is satanic. From the secret anger to the act of murder, the fleeting glance to adultery, the covetous look to idolatry, it is sin.
We all know the Biblical account of how sin came into this world. God gave Adam and Eve all of the fruit of the Garden of Eden for food. Except for the fruit of one solitary tree that stood in the center of the Garden. And as Bill Cosby so succinctly put it, "Adam asked, 'Now which tree was that?'"
Actually, that is not what happened. Adam and Eve were not looking for an opportunity to disobey their Creator. They had the ability to obey Him and the ability to not obey him, yet they were not looking for a way to exercise their freedom to disobey. They were tricked. And yet they were tricked in such a way that they knew exactly what they were doing. There was no slipping into sin. Through the serpent's deceitful words they were seduced and then knowingly disobeyed the very words of God.
Similarly, there really is no slipping or stumbling into sin today. Rather, "... each person is tempted when he is lured and enticed by his own desire. " (Jam 1:14) Two things about our desires,
1) We know what we desire. We do not desire that which we do not know. I do not desire anything that I do not know exists.
2) We do not desire that which is unpleasant. We do not desire torture for ourselves. "Why do some people desire death? Death is unpleasant" you say.
Yet for the person who desires death, death seems preferable to them. They think, "Why continue living under such hostile conditions? It would be better for me if I were dead." I do not want to offend anyone with this language, but want to make the point that we all do exactly what we want to do. We explore our options and then do what seems preferable to each and every situation.
So it was with Adam and Eve. At first it seemed preferable to them to abstain from the fruit of the tree of the 'knowledge of good and evil'. They associated the tree with death and punishment. Then the serpent arrived. Through enticing words he made the tree seem preferable to whatever punishments God had imposed. He made disobedience to God seem preferable to obedience. And with eyes wide open, Eve took of the fruit and ate. She then gave the fruit to Adam, who also knew that this was disobedience to God's command, and he ate. As they ate they came under the judgment of God.
Thankfully, that is not 'the end'. God did not leave Adam and Eve to die alone. Instead, he already had a plan in place for the salvation of mankind. In fact, the temptation, the fall, the judgment, all was God's plan.
Adam and Eve at this time begin to see God's plan coming to light. God has something better for them and for us. Something better than Eden? Absolutely!!! Something better than innocence? Yes!!! The beginnings of the this something better are revealed to them in and imperfect light, but clear for us to see:
The LORD God said to the serpent, "Because you have done this, cursed are you above all livestock and above all beasts of the field; on your belly you shall go, and dust you shall eat all the days of your life. I will put enmity between you and the woman, and between your offspring and her offspring; he shall bruise your head, and you shall bruise his heel." (Gen 3:14-15)
It is the Gospel.