Basically, you don't have to put things as "simply as possible" for mine sake, unless your doing it for some other reasons.
But yes, good point: reasoning and decision making does largely consist of two reference points, whether right or wrong, better or worse, accurate or less accurate, beneficial or not so beneficial, true or false, safe or unsafe, etc. The difficulty though remains in knowing to what extend Adam and Eve were morally conscious creatures and what was the state of their intellect. Perhaps it's as simple as that it was the beginning of the creation of heaven and earth, and thus wisdom and knowledge did not yet exist on earth, but in heaven only (that is the spiritual realm, not the visible heaven created for the earth). Therefore it was God's plan for mankind, by pure and unobstructed fellowship with Him, to be brought up in all wisdom, knowledge, and the understanding of every right way and good work - the way of life and good, even as He Himself made all things very good. This is even seen with God placing Adam in the garden at the beginning - essentially safeguarded in paradise - so that by maturing in understanding and the knowledge of good (see 1 Corinthians 14:20 and Romans 16:19 for reference) they may multiply and subdue the whole earth, and exercise dominion over all the creatures. But this was all brought to ruin when they, being deceived by the serpent (that is the Devil), thought they can be made wise themselves apart from God, breaking His commandment that served as their life and for their good; similar to how children are forbidden certain things without an explanation given them, for the simply reason of them being still children. And with this transgression followed all sorts of evils, curses, calamities & sorrows, and most importantly, corruption and death. (And as a sidenote, why do people even burden themselves with knowing the depths of Satan [Revelation 2:24], seeing it is a "bottomless" pit? [Revelation 9:1])
Now I know you like keeping things simple, therefore the main point I was trying to get at was this: it is inaccurate to think that they must of been acquainted with both good and evil before their fall, because before their fall (regardless of how long that may have been) they would have been brought up by the Lord Himself in refusing the evil and choosing the good (see Isaiah 7:15 for reference).
