oh, you've confused me now! Are you asking me what a hair shirt is? Bc I assumed you would know. I'll post a short piece about it but apologies if I've misunderstood and you know this already.
It's not limited to the Catholic faith, afaik, but it certainly figures large in the history of the Catholic church, especially nuns (and presumably monks, also). Self-mortification and all of that. I can't be doing with it. Someone isn't holy or blessed bc they have cancer. They just have cancer. I think the basic idea exists in certain Buddhist practices but I don't know too much about that, I'm more familiar with the Catholic story. It's a good example, imo, of the difference between the faith and the church. Or faith and organised religion.