Birthday's were a huge deal in her childhood, so now she treats birthdays in her own family like they are sacrosanct. A few years ago, my brother and I did a big backpacking trip that we had been preparing for and dreaming of for many years. This trip happened to fall during their twin's birthday. She was livid that he would dare to be gone on their birthday, even though my brother had planned to more than make up for it. The date is what worked for my schedule and it was a perfect time to travel through the area that we backpacked through. It has been almost 4 years, and I still don't think that she has forgiven me.