Both keep honest people honest.
Strong passwords ARE better than weak ones.
We say it is easy for someone who knows you to guess passwords. In researching this topic I set up a test. You could say they were not good at what they do - they are. Much like those brain teasers. This is not to suggest that people should pick passwords easily associated with themselves, only to suggest that security people may be doing a disservice by running password crackers and enforcing absurd formulas.