@awnlee jawking
That's just bad writing.
It's like writing a story with advert breaks, where the advert is for an unspecified future part of the story.
I am likely to consider it bad writing if it is a reveal that the reader doesn't expect.
I have a story about soldiers in the US Army during World War Two, focusing upon the ETO (European Theater of Operations); but early in the story I depict the USA before the war. So, when a young soldier takes his first ride on a train, he compares the luxury of the City of Los Angeles (in 1939 the premier service) to pictures he has seen of ocean liners (something many readers have probably seen depicted). As narrarator I mention that when he will eventually voyage on an ocean liner, it will not be luxurious at all.
The blurb of my story is explicit that the Amphibious Invasion of Normandy will be a major event in the story. So, I am not "giving away a secret"; I am contrasting the opulence of that peak of railroad travel in the USA. Few people know what railroad travel was like in the USA in 1939 (fastest and more luxurious than in the 1950's, let alone the 21st century) but most people have seen the movie Titanic.
Since the readers know the characters will be traveling by Ocean Liners converted to troop ships. Probably what I am doing is Forshadowing.
My example may not be the best. However, some authors do use the technique well.
The various books of Variations on a Theme, uses this technique from time to time. Since several characters are aware of events of a future, yet are aware they are living in an almost identical world to the futures they knew, and yet there are several personal and historical events different from what they knew before. The characters reference what they anticipate as they make their plans; also informing readers of events they might not be aware of, to give context to the plans and actions of the characters.
Any other examples of how this technique could be used effectively?