Why can't I see the abandoned cart in Magento for an email that MageMail sent?

A lot of times you might not be able to find an abandoned cart in Magento for a corresponding Magento abandoned cart email that went out.  This is because MageMail captures more abandoned carts that Magento does.

For example, guest orders that are abandoned or even if the customer only enters their email address and never even progresses far enough in the checkout for Magento to capture the email and save it to the quote.