What is the fine-grained topic of the following text: In An Unquenchable Thirst Mary Johnson shows true courage, not just for leaving the Missionaries of Charity after twenty years but for being willing to talk about the difficulties of MC life and the troubling nature of closed systems, absolute obedience and the deep futility of choosing suffering for its own sake. Only return the topic.
Mary Johnson's courage and critique of life in the Missionaries of Charity as depicted in her book "An Unquenchable Thirst".