Because of course, if a person guesses one, they'll gain access to everything else. Especially risky if you own accounts that have sensitive information, like saved credit card info.

Instead use a program that saves all your passwords, like Password Safe. It lets you organize your passwords into categories. It's a lot better than saving your passwords in a Word or Notepad file.

Worth giving it a shot:
http://majorindulgence.com/u/44