A perfect example of this is Pat Rothfuss's King Killer trilogy. *Spoilers ahead for the first 2 books* Rothfuss sets up Kvothe's story as a story literally being told in the book. Present day Kvothe has become an innkeeper by the known by the name of Kote and Chronicler has come to hear his life story. At the end of chapter seven in the first book, The Name of the Wind, Rothfuss tells us most of the promises that he will pay out over the course of the story.
"I have stolen princesses back from sleeping barrow kings. I burned down the city of Trebon. I have spent the night with Fellurian and left with both my sanity and my life. I was expelled from the University at a younger age then most people are allowed in. I tread paths by moonlight that others fear to speak of during the day. I have talked to gods, loved woman, and written songs that make the minstrel's weep.
You may have heard of me." -The last 2 paragraphs of chapter 7 in the Name of the Wind, by Patrick RothfussHere you can see that Rothfuss has made a promise to his readers. There will be a princess who is stolen, perhaps an implicit rescue. Kvothe will burn down a city. He will explain who Fellurian is and Kvothe will spend the night with her. Kvothe will go to University and be expelled. He will talk to gods. The name of the series is a question the book must answer; The Kingkiller Chronicle. We learn that Kvothe is living in isolation and he's lost his magic. For the story to be complete we should have most of these questions answered.
In the first book we learn that Kvothe is accepted into the university. We see him burn down the city. The genius of the story is that even with such bold promises, "I burned down the city of Trebon," Rothfuss pays them out in unexpected ways. Trebon burns by accident and Kvothe all but kills himself trying to contain the fires. In the second book, The Wise Man's Fear, he reveals the story of Fellurian and he opens more questions. Why does Kvothe feel responsible for the war? When the third book comes out we should receive the answers but the questions keep the reader interested enough to move forward in the story.