Are chain letters true or forwards?

I was just wondering this because i get a lot of forwards and chain letters sometimes and they irritate me like crazy. Like every time i see them on facebook like if someone left a chain letter as a comment on someone elses wall and i and i see it i have to fwd it cause i feel like if i dont post it to someone eleses wall i will have bad luck. I also have OCD (Obsessive Compulsive Disorder) which makes me worry about things and stress over stuff i do take meds for it so its not too bad. please tell me if chain letters or forwards are true or not because that will help so i dont worry. thanks:)