Foreshadowing, for those that don't know, is when an author uses words or phrases to hint that something is going to happen that involves that. The most famous, and the clearest, form of foreshadowing that I can give, is in Flannery O'Connor's short story, "A Good Man is Hard to Find". I had to read this book in a Study of Literature class in my second semester of college.
Everybody in the class agreed: the ending to the book was terribly unexpected, but if you actually read the text, the author gives a very clear hint about what is to happen later. There was no other way that the book possibly could have taken after that simple hint was given, otherwise the story would have been plot-less.
Another form of blatant foreshadowing was in Christopher Paolini's first book, Eragon. Halfway through the book, the title character goes to see an herbalist, Angela, who tells his future. It is given in great detail, and the fortune telling is done using magic, so it's revealed that it has to be true.
Despite my rather vulgar feelings about Christopher Paolini due to his last two books, (because we all oh so believed that relationship was genuine, and trilogy my butt!) this was a clear example of a cheat sheet, and a bad one at that. You don't even have to read the books that came after to figure out what they would be about if you are clever enough; he spells it out in that one chapter.
I understand that it could have been used as a way of ensuring that there would be later books, "Hey, I said there's going to be some pretty cool stuff going on later, so make sure you let me sell them." But to me it just seemed like he needed a guide for his book to go along, and writing has always been about fluidity to me. If you have your book on a rail without any room to deviate, it just seems rigid. That's why the relationship between Eragon and Arya always seemed less like an epic romance and more like the kid who gets a valentine for the first time and then thinks they're dating.
Well what is good foreshadowing, Jacob? You might ask me sitting there, reading my rather inept explanation as to why foreshadowing is bad. Well there is such a thing as foreshadowing. The color red come up several times, before a man is killed and lying in a pool of his blood, is decent foreshadowing. Having a woman wake up and not be able to hear any kind of noise prior to an actual world ending event where the entire world is silent, that’s good foreshadowing. Foreshadowing is always best when you have to go, “Oh wow, I should have seen that coming.”
Foreshadowing should never be used as a cheat sheet. A good story should be able to stand on its own merit, as an individual tale that does not need a crutch to hold itself up