I’m a great believer in foreshadowing. Done well, at an appropriate time and with subtlety, it positions the reader to accept something that happens later in a story. Without it, the reader may be left shaking his or her head and asking “where did that come from?”
For example, in my current project (Empty Luck), I introduce two brothers, the Sullivan brothers. Tommy, the older by three years, makes a dangerous and criminal decision that requires the participation of his younger brother, Ricky. Logically, Ricky, a new police officer, would refuse to take part in a crime, but he gives in.
Why? Well, by foreshadowing earlier in the book that Ricky has always looked up to his older brother and admired him, despite his objective faults, we can believe Ricky might well agree. In fact, we see early on that in some ways, Ricky would like to be more like Tommy, more fearless and more confident, as he perceives him. Whether Tommy really is confident and fearless is another question, but even at 26, Ricky still views his big brother with childhood eyes.
So we learn this about Ricky early on and therefore following his brother later, as an adult, make a kind of believable psychological sense.
The goal of foreshadowing is for the reader to be surprised but then to have a lightbulb of understanding click on. They figure out from the earlier information that yes, this odd decision is after all, plausible.