am not going to wear a hair shirt

For anybody like me who was entirely confused by that sentence:

A hair shirt is a coarse garment intended to be worn next to the skin, keeping the wearer in a state of discomfort and constant awareness of the shirt’s presence. Such garments were traditionally worn by some Christian religious orders, along with individuals who felt penitent about certain actions or their lifestyles. Their use is fairly limited in the modern era, but the term is often used metaphorically, which is why someone might refer to “wearing a hair shirt” when they perform some other act of self-imposed penitence.

https://www.historicalindex.org/what-is-a-hair-shirt.htm