For us it was my Uncle Charlie's "Dear diverse Kith and Kin" letter. I think it was the thing mentioned the most at his wake, how much we would all miss his yearly missives.
I have written a Christmas letter or two..but they never go out..I'm a flake.
This year, my cousin Bob (Hi Bob!) inspired a simple yet way longer than I anticipated Christmas letter. I have to have Big Daddy read it for approval (and editing because I ALWAYS make silly mistakes) and then, since I already have the Christmas cards AND this years Christmas ornament (I make a themed one every year) I think I might actually get them all out...and maybe even BEFORE Christmas. Go me! lol
