How many different online accounts do you have? Online banking, e-mail, social websites, etc. Add on to that all of the online shopping sites, and you're probably over 20 at least. How do you remember the passwords? Some people use a single password for every site. That's NOT a good idea. Take a look at the linkedin security breach a few weeks back and you can see why. If you used the same password for LinkedIn that you did for your e-mail, the data thieves now have access to your e-mail, which will pretty much give them access to nearly every account you have.
So what is the solution? You should have a different, hard to guess password for each site. To keep track of these passwords, you should use a password manager.