I think that I've solved the mystery of having periods. You don't actually lose an egg or two in the process, what you're actually losing, are brain cells, which is why I'm getting dumber and saying more stupid things as I get older. Also, after your period, your mind adjusts to having a few less brain cells and you talk like you normally do. When you get pregnant, you actually hold in all your brain cells until that final push, then you push out nine months' worth of brain cells.
Why do I say this? Well I just insulted our finance officer and I'm blaming it on my period. I told her I thought she was older than I was, and her driver's license told me that she's actually about 3 years younger. Oops.