Curses do exist as they involved in witchcraft and supernatural things! I mean science does not prove anything! Science is just full of theories! It is ridiculous when people say "Science proves that God does not exist" they cannot fully prove the creation of Earth. Science is just like Religion.
Curses do exist in many different forms for many different reasons. There are different spirits and gods that the people of this earth believe in, and if you believe in anything long enough, it becomes real to your own mind. Curses are the same way. If curses are believed in, they have the potential to become real.
It depends on cultures. Some cultures believe in it and some do not. Whatever is the case, I do feel that Curses actually exist. If one knows that one has been cursed by someone, there is a high possibility that it would affects once psychology and one will experience an impact of the curse for sure.
As a scientifically-minded person, I do not believe that curses exist because they've never been proven in the lab. It seems much more logical to me that people prescribe curses to themselves as a way to explain a series of random, unfavorable events. It can be more comforting knowing said events weren't random. And believing it was a curse also likely leads to believing it can be broken, giving the believer a sense of control over events science would deem random, or unrelated.
Curses exist in the form of cause and effect, not spiritually. For example, you kill someone, you are "cursed" with guilt and punishment, you are "cursed" with death. Things will happen for a reason. One does not simply wake up one morning after living a kind and rewarding life, take a drink of water sit up and become "cursed" randomly by an unrealistic spirit or god.
We are more powerful than we give ourselves credit for being. Our minds can more or less control how our lives go. If we feel for some reason that we are cursed odds are it will seem that we are cursed. But does a curse of someone saying that have put a curse on us actually exist, that is unless the person believes in the curse itself.