It does not matter how big your dictionary is. Even a brute force attack with limitless tries allowed could take an unfathomable amount of time if a password is strong enough. Look at the site I mentioned above about the estimated crack time of any password. I tried some passwords with the formats I usually use and almost all of them would take an infinite amount of time to crack with a brute force attack.
You should also understand that it's not just guessing the password that matters like @BoazKE has alluded - - you must also bypass the security measures employed by the password authentication mechanism. What would you do if you're locked out after trying to guess the password twice?