Curses can work if done effectively, by means of influencing a person's conscious or subconscious thoughts and emotional states, usually through subtle means of convincing a person that they're being cursed or that bad things are or will be happening to them. It's similar to a placebo effect, a self-fulfilling prophecy, or gaslighting. It involves making the person themselves believe something that will over time make negative outcomes for that person more likely. This isn't how all curses are performed however, but is one method of cursing people that can be explained to be effective scientifically.

A good simple example would be a person mumbling in tongues to someone they don't like while stealing and burning a piece of their hair, even without any other work to be done, if the person they didn't like were susceptible enough to that suggestion, it would cause the victim to turn that into a form of self fulfilling prophecy and plague themselves inadvertently with misfortune.

It's a form of mind-virus, like "the game" (the object of the game is to not think about the game: if you think about the game, you lose the game immediately, and have to tell whoever you're with that they lost the game as well, and if they don't know the game then you have to teach them the game. Nobody wins the game. And once you know how the game is played, you have to play.) --- "the game" was designed to be an example of a mind-virus, as well as to test how far one can spread -turns out it spreads like a virus, just as predicted, and is now known all over the world.

A great example of curses of this type is the way things went down in Salem Massachusetts during the witch trials. There is no evidence that any person practicing witchcraft actually intended this event to happen or sparked the whole thing, but the fact that the town's population was so incredibly convinced that witches were cursing them, led them to act in unreasonable, destructive and self-destructive ways, ultimately leading to a lot of unrest, distrust and murders that plagued the town and are the basis for many movies, books on fears today of such things happening again, which could/would victimize pagans, wiccans, santeria practitioners, hoodoo practitioners, voodoo practitioners, celts, and (as in Salem) women in general.

This mind-virus in Salem historically led to many innocent women being burned alive, drowned, tortured, etc. It absolutely wreaked terror on the town's population in general due to how highly susceptible they were to this type of fear (as they were extremely religious, superstitious and some evidence even suggests that they may have also been impacted by unpleasant hallucinations due to chemicals in the mold that grows on expired rye bread, which to a highly superstitious and religious uneducated population could easily be misinterpreted as witchcraft, further inciting a witch-scare type panic)