Why does Roan believe they need to accept the Darkness and whatever is added to it? The answer actually came from Sister Orb once they noticed the effects the Darkness had on the mind.
[That's weird. If this Darkness is truly having such an effect on your mind, that also includes the soul. The System protects all four of your souls against anything harmful. If the System isn't doing that now, then is this environment really harmful to the mind?]
Indeed, since the system isn't protecting them against it, it is because it can't truly cause any harm. That's how the system worked, and although the twins wouldn't simply believe it was infallible, it still hasn't given them a reason to doubt its soul-protecting power.
So, Roan's orders were very clear once the time arrived, just accept everything.
