Foreshadow is the hints and clues of what is to come. Sometimes in a short story, they don't come at all, while other short stories use them so much, it puts the reader on edge, anticipating something big.
It is, in a way, a form of manipulating the reader into investing themselves into the lives of your characters. A foreshadow that is well done will have people guessing at what is to come. A story well told will have the readers churning the story over in their mind for days to come. Foreshadowing is a great tool to do that.
Is there such a thing as too much foreshadowing? Can you go overboard. What if you can't live up to the expectations of the readers? What if they are left waiting?
The story blog, This White Wardrobe, is a prime example of a story that could go either way. There is foreshadow in every post, of what was before that was unexplained, and what is to come that is unexplained. The reader gets the sense that at some point, the past will be explained in full, and the future will be discovered. The only way that this overuse of foreshadow could fail is if those explanations never come, or if they have no intrigue and leave the reader's desire for suspense unfulfilled.
The overuse of foreshadowing will not work in every short story or novel. It works in some because reality is skewed in many stories. The more skewed reality is, as in the closer to a wild fairy tale that the story becomes, the more use of foreshadowing is appropriate.
Foreshadowing can be ignorance and curiosity. If a character just doesn't know something, but desperately wants to find out, this is the most natural form of foreshadowing there is . This thing that they do not know becomes an obsession, and they spend all together way too much time trying to figure it out. The story may not present itself as a mystery fiction piece, but it is that in reality.
There is certainly a right and wrong way to use foreshadowing. If your story captivates the reader, you don't need to worry about how many times you are using each literary element. For many, this process just comes naturally. For many others, you will need to map out each story, consider how much of this and how much of that you will need. It will be like closely following a recipe for you. Just don't let your readers know that is what you are doing.