Having a strong password can save you a lot of pain and even financial loss. Imagine your password being  12345678. Imagine your FB being breached. When some of the passwords were leaked on a popular site due to a security breach, analysis of those gave startling results. Believe me or not, some people still use easy to guess passwords.

What is a strong password?

As per Microsoft password checker, strength of a password depends on the different types of characters that you use, the overall length of the password, and whether the password can be found in a dictionary. It should be 8 or more characters long.
See this password strength checker from microsoft: https://www.microsoft.com/security/pc-security/password-checker.aspx

As per a security firm analysis, most common passwords were:
1. 123456
2. 12345
3. 123456789
4. Password
5. iloveyou
6. princess
7. rockyou
8. 1234567
9. 12345678
10. abc123
See here for more details: http://www.cxo.eu.com/news/password-protected/