Your password is "validated" when created. Validation means checking if it contains (it has to to validate):

 * a alpha character in it
 * a numeric character in it
 * a special character in it 
 * (maybe more, this list is from memory)

This means if you want to brute force such a password you do not need to check any password that does not follow the above mentioned rules. This makes the search space smaller and the cracking of the password faster.