first I'm not discussing religious here in this topic.
long before christianity , people set december 25 as the birth day of sun-god Mithra . after that people set this date as birth day of jesus .
let say if the Mithraism also with same reason setting this date as christianity . is it possible that people have celebrating on this date long before Mithraism but with different reason ?
i feel that we forget what actually had happen on this day in long long past but we past down the date from generation to generation.