AviD's Rule of Usability:
Security at the expense of usability comes at the expense of security.
Taken from: Security StackExchange
[http://security.stackexchange.com/questions/6095/xkcd-936-short-complex-password-or-long-dictionary-passphrase?newsletter=1&nlcode=390222%7c5068]
Very accurate and a good KISS [https://en.wikipedia.org/wiki/KISS_principle]
-message in there as well