When Abrogail Thrune turned 16, shortly after she became a second-circle sorcerer, she looked at the Chelish Empire, which she intended to rule someday, falling around about herself; the provinces of Andoran and Galt, that should have been hers, already lost by her incompetent uncle.
Abrogail knew that as a second-circle sorcerer she could not take the Crown of Infernal Majesty from Infrexus. Even executing a compact with Asmodeus would give her two more circles at best. Infrexus had held five sorcery circles in his late forties, won of the Worldwound and a few years' adventuring, when he executed his own compact and took the throne.
So Abrogail went to Hell, living.
She asked the devils there to fight her, and heal her when she fell, and put her to sleep when she had no magic and needed to regain it; and punish her for failing, for losing, to make sure that when she fought she did so desperately and in that state of stress that is conducive to absorbing magic.
She wanted to make it to seventh-circle, so she could be ninth-circle after executing her infernal contract.
Abrogail tried. She tried really really hard.
But when even her will broke, Abrogail was only sixth-circle still, and so is only eighth-circle now.
It's a very efficient way of leveling. If you ask why not everybody does it, it's because that would shatter almost any mortal's mind like glass. The Thrunes have a touch of Hell in their bloodline, from which their sorcery comes, but even among them, the reason why only Abrogail did that is that only Abrogail could.