No sane person would ever like someone else reading her email. Or for that matter some other person using her password and breaking into a financial institution. You should, therefore, choose a strong, secure password in such a manner that would be a hard nut to crack for others and easy for you to remember. The more random and mixed-up you make it, the harder it is for others to crack. Mind you, if your password is compromised, the password crackers will even take over your identity.
A password, if too short, is vulnerable to attack if an attacker gets hold of the cryptographic hash of the password. Present-day computers are fast enough to try all alphabetic passwords shorter than seven characters. We can call a password weak if it is short or is a default, or which can be rapidly guessed by searching a subset of all possible passwords such as words in the dictionary, proper names, words based on the user name or common variations on these themes.
On the other hand, a strong password would be sufficiently long, random, or which can be produced only by the user who chose it, so that ‘guessing’ for it will require too long a time.
For maximum...