Stupid dick. Why would you try to make smart, well thought out decisions if your destiny is already determined? Your decisions have no impact. Hope this helps, ginger pizza face 
Woah! A Jess Z sighting!
Even though your destiny is determined, you would want to make smart, well thought out decisions to avoid immediate harm/trouble to yourself/others. Just because your life may be messed up, doesn't mean you should throw caution to the wind and endanger others.
Someone who drinks and drives would be an example. If someone thinks there is nothing left in life for them, because of destiny, and then decided to just get drunk and drive home, because there's nothing left to live for, this would endanger others. And this would not be a smart, well thought out decision.
Jess, just because you think your destiny is set, this doesn't mean you should keep living the way that you have been recently. I think that you should try to clean up your life. Find a way to stop living in your car, get off of the methadone, and maybe make amends with all the people that were hurt by your past decisions. Don't be ashamed to ask for help. There are public resources available for people like you. But don't ask me for help, though. I don't help people who are able bodied, yet don't want to help themselves.