The ingénue's weakness is grief. Some trauma in its past renders its memory and history abominable to it. It may follow any number of paths—servitude, rebellion, self-indulgence, self-mortification—but the goal is always the same: to involve itself so deeply in the present that it has no time to remember the past.
In the summoning contest, the sorcerer plays on this weakness, forcing the demon to dwell upon the pain it spends its life struggling to escape. Then, when a new history empty of trauma is laid out before it, the creature willingly flees into the labyrinth of its bindings.