There's something about knowing a secret that makes you want to tell everybody about it. Personally, I don't think I have any secrets of my own, or at least I can't think of any right now (... there goes my mysterious womanly charm out the window!), but I do know that if , for example, I know the result of a particular sports game, the ending of a book, the plot of a movie etc, and I know that the other person is still waiting to find out for herself, right away I get this terrible terrible itch to spoil it all!
I do think I'm pretty good at restraining myself in these situations but it sure does take a toll on the soul. ;)