The explanation is this. Weak passwords use letters and numbers. Programs exist and have been in the hands of hackers that search for letter number passwords quite well and don't take that much time to do the searches. Those extra symbols the programs don't search for. That puts passwords with the extra typing symbols in a stronger position, hackers can't get into your system as fast. That gives you more time to take defensive measures when you detect a hacker attack attempt. Let's just say where I work this is justifiably a big concern. How do you detect a hacker attack? Logs should be written to with every attempted connection to your system. In those logs failed connections are listed as well as successful connections. If you read failed connections on your system at dates and times when you weren't using the computer, someone else was trying to do so. That ranks as a possible hacker attack attempt.
