This is how curses work in my opinion:
It's the power of the mind. For example: (I'm going to use names to make it less confusing.) ok, Lets say the Sally put a curse on Mike. Sally put alot of effort into her curse and she truly believes that it will curse him.. And once Mike finds out that Sally cursed him, he will get paranoid and bad things will start to happen. It's The mind is very powerful thing. So if someone says you are cursed just shrug it off because if you let it get to you the curse will work. I really believe in the power of the mind is a VERY powerful thing.