The Art of Decluttering

The art of decluttering is the stuff of books.  And dreams for most of us (although there appears to be a growing genre of books about the joys of having lots of stuff with nowhere to put it). 
I recently spent a weekend at my mother-in-law's house helping her to get ready to put her house on the market and move to a smaller and hipper apartment.  Lucky for both she and I my husband and his three siblings joined me in this endeavor, and the subsequent stress made me think.  This really is not easy.
Why is that?  One thing is that I think it can be hard to have perspective on what is worth saving and what is not.  I was talking to my parents about things that they have found since they have moved and are unpacking.  My mother's mother's birth certificate is one such item that had some surprises.  While my grandmother was legitimate (yes, this is noted on her birth certificate), she was the third birth to her mother, who had only one sibling to our knowledge.  She also was named Hortense, like her mother before her.  She went by Josephine (her middle name) and who can blame her--why would a woman who was already saddled with the name Hortense give it to her daughter?  And why her third and not her first?  And what happened to the first?  But ultimately, why even keep this?  Maybe it is just really hard to let go of one's personal history.