"A magic book will vanish if it harms its master."
The magic tome lore in this work is especially stifling (that is, serving the plot). How do you even define what harms someone and what doesn't? Aside from really obvious cases, it would largely depend on the person. An SJW type of person would feel greatly harmed by the most insignificant of insults, whereas a really competitive and ambitious person would be okay with everything short of grievous permanent wounds if they could learn powerful magic from the tome.