Remember when Miley Cyrus had all them photos leaked of her from her email account? Well it was because the hacker was able to find her date of birth and the name of one her dogs. The password just happened to be {dogsname}{year of birth} thus, the "hacker" got lucky, got in and found a glorious amount of... photos.
In short, the moral of this fun fact is the password should have no personal link, or anyway for someone to be able to guess it by knowing you... or in some cases what Google knows about you.