Both my father and my mother in-law hoard in a big way. In the case of my father, it's to the point where he won't give me my inheritance from my great-great grandmother even though the deal was to give it to me when I bought my first home. My mother in-law's case is a bit more pronounced. She has several rooms that are completely unusable, but she is also realizing what a wonderful home she could have and is working hard to clean the public portions of her home before cleaning the more private areas.
If I said that I was understanding of both people in my life, I would be lying. I was not able to understand how objects could have such a strong meaning that they wouldn't be able to give up items. For example, I can remember when my mom got rid of a bunch of porn magazines under the bathroom sink because my sisters and I were getting older and my mom didn't want us to find these magazines. My dad was angry to the point of making myol mom think he threw away two of her collections which occupied the living room. I never understood how he could equate old magazines hidden under the bathroom sink with collections on display in our home. Now I think I understand.
Whether you know someone who hoards or are interested in the psychology of hoarding, this is a good place to start.