Well its different for everyone, but for my wife and I, its because it was my sons birthday. He died 3 years ago, and its just a reminder that he is no longer here. I will never have Grand kids, I can never have any contact with my son again. So if you see someone who is not in the mod to celebrate, maybe they have a good reason. You never know what the person next to you is going through in there life. RIP my son.
