God the Father created the world but did not complete it. He left that task to man.
Now there is an optimal speed at which the improvement of the world and every man’s character ought to proceed. This speed is finite and determinate, because man can use his powers for both good and evil, and if God had increased the human power to improve things, then his power to worsen things would have increased disproportionately; conversely, if God had weakened man’s power to destroy, then his power to create would have diminished disproportionately, as well. Man then is optimally built.
Now pick an arbitrary guy on the street. Does he over his life of 80 years have a chance in hell always to improve most efficiently? Surely not.
We must needs suppose then that God placed the first human being, “Adam,” in the best external environment to see whether he would keep completing and perfecting God’s creation at the optimal or best possible speed. We are not told how long Adam was supposed to stay in the Garden before he would be allowed to procreate; perhaps a year, perhaps 5 billion years. Regardless, Adam failed to develop optimally, and, having seen this failure, God no longer found the creation beautiful or worthy of His graces. He withdrew and forsook the first family and all their descendants.
Perhaps, the original creation was so good that Adam, Eve, and the Garden were indeed all created 5 billion years ago along with life as such, and it was going to take that long for the “probability” of Adam’s sinning at least once to reach exactly 50%. It is too bad he and we got unlucky.
As per the previous post, Adam’s sin was contingent though determinate event. God foresaw it but decided to create anyway, having located a remedy for it through the Incarnation and all that followed it. To be more precise, the Son persuaded the Father to create after agreeing at the outset to undergo the trial as Jesus.