Deltiology 101: reasons to keep postcards

My mom just gave me a postcard that I had sent her in 1985.  She kept it for 28 years.  She didn't remember if it was because of the tender message, or that I was apologizing for something, or if it was because she's a pack rat.  Either way, I'm so excited that she gave it back to me.  I'm choosing to believe she saved it because she is deep down sentimental and knew I loved her despite all the grief I was giving her.