And so God said "let there be Valentines"

So...I have become quite predictable, normally I would suggest that Valentine's day is a prefabricated holiday invited by the greeting card companies, however i don't tend to agree with such a radical statement.  When I was in grade school our parents and teachers would suggest making valentines for all the other students in class, but why is this so? At that age how could you even know what love is? The majority of the people I know don't even observe the day.  I suppose I could sound a little bitter about the whole thing since I've been single for awhile, although this is the one day out of the year where everyone is suppose to "have someone".  But everyone who doesn't "have someone" is now depressed  because one stupid day out of the year says so.  So now I'm back in grade school and I'm the only one who didn't get any valentines.  I would like someone to explain why to an eight year old.