I actually like birthdays and the idea that everybody has this one day that is about them, a 24 hour vacation where you can put yourself and your desires at the center for once. If you have a party, you give pleasure to all your guests as well and it is more of an excuse to meet up than about you.
This!
I think each having a personal "holiday" for ourselves is a good way not just of marking time during the year, and of marking your own age (think of how much harder it would be to compute your exact age if your birthdate were of little importance), but also is good to have a time of personal grounding in terms of looking back on previous years and looking forward to the next one. It is a compartmentalization and division of your past, present, and future... the New Year is a similar concept, but that is a largely social/communal holiday, with the idea of personal
improvement, while a birthday seems more reflective in nature. More about everyone celebrating
for you instead of
with you, and more about you looking forward to another year, instead of making changes for another year.
Plus, it seems socially useful for each person to have a special day on which they should be particularly recognized. It encourages us (in particular if you use Facebook) to attend to that singular person on that one day, and thus helps stabilize our social webs. It is not too much to be asked to remember someone once a year, but remembering someone once a year is enough to maintain loose ties. And if they are closer, it is an opportunity to demonstrate caring, compassion, and empathy towards them in particular. It's sort of like how you want to have a special date night every once in a while in a relationship - it spices things up and lets you devote extra energy to that one, not-very-often night... provides both variety and relief, so you don't have to work so hard to attend to them and your relationship the rest of the time.
And, at least for me, it is a lovely psychological departure from the middle of the cold, gray period between late winter and early spring.
From a sociological perspective, they usually aren't.
Was this rational?
Actually, not to be a dick, but it
was, since they believed that the heart was part of the sun and taking it out was returning it to its rightful place. Plus you were rewarded with a better afterlife if you died in an "honorable" way. And the common beliefs included needing to sacrifice to the gods to maintain good weather / fertility / lack of natural disasters / etc., so it does really make logical sense to do that, in those cases. As for the logic of those beliefs themselves... science is unfortunately trapped in its time... so I figure they were probably doing what seemed reasonable with the information they had...