OK so I reread this section again. The part that threw me off was the mention of taking damage. That refers to the characters lore die increasing. The sections Using Sorcery and Facing Monsters is oddly placed and interupted the explantaion.
Ok, so the mechanic is built around a Will save. (something else I missed the first time.) If that save is failed then the category is opened or the die is increased. The rules are a little wordy in that they say increased by 1d10. This is not a physical die roll of a d10. The category instead is opened up at a d10 and then increases by +1d every time that Will save is failed in the future. When the dice chain gets to d30 the character has gone completely insane. Before then though the character has gained more knowledge on the subject and can use their category die for skill checks instead of the untrained d10.
You got it! While corruptions mutates the Wizard, I felt the Sorcerer needed to have Madness be a factor as well. You can ultimately learn the secrets of Leviathan, however this leads down the path of Madness.