Basically if the nervous system is damaged and fails to send a message to the brain the brain doesn't have a clue what's happening. The nerves don't think on their own which is why the message must get to the brain to be thought about or interpreted.
If you have no feeling in your foot your brain has no idea if your foot is being touched, if your foot is on fire, if your foot is getting cut open, etc.
The message has to get to the brain otherwise you don't know what's happening. Your foot can't tell you what's happening. It can't think on its own. It has to deliver the message to the brain. If the brain doesn't get the message for whatever reason you will have no thoughts about it whatsoever. The message won't be interpreted or received somewhere else. It must get to the brain in order to be acknowledged on a conscious level.