3 Reasons Why You Remember Someone's Birthday

I guess there's only 3 main or obvious reason why a person will and can remember another's birthday.

Reason #1 - You Care About Them!!!
The logic is very simple. They are your best friends, someone you really care about, somebody you really close with at school or at work, or even he/she is the person you like/used to like. :P

Reason #2 - Their's close to your's
And again, simple. Perhaps their's fall on the same month with you, or within a week or two from yours, that's why you remember it. ;)

Reason #3 - Facebook
Do I really need to explain this? ~.~