Foreshadowing

I think of foreshadowing as similar to planting a clue or misdirection (red herring) in a mystery story – you don’t want to be to overt when you do it. Foreshadowing is the subtle positioning of information that usually serves two (or more) purposes.
The first purpose is to provide information relevant at the part of the story that is being told.
The second purpose is to explain something that happens later, for which an explanation at that point in the story would significantly disrupt it.

Here is a simple example from my Finger of Suspicion story.

Early on, I wrote "Kelly fingers, their nails chewed to the quick,”…

The first purpose was to tell the reader about Kelly – anxious, a nail biter, not in a position to be concerned with her looks.

This is then compared (though not specifically) with the long painted fingernails of the kidnapped heiress and finally revealed as the reason Kelly retains her digit (and perhaps her life).

Franklin explains foreshadowing on page 150 of ‘Writing for Story’ as “the technique by which the writer unobtrusively inserts details early in the story that will allow him [or her] to conduct his [or her] dramatic scenes without the necessity of explaining the background details.”

Franklin says that the principle was codified by Anton Chekov as Chekov’s Law, which specifies, “if the opening of a story mentions a shotgun hanging over the mantel, then that shotgun must be fired before the story ends.”