As we drank our Irish coffees, we discussed the ideal answer to any reader inquiry, which boiled down to, "Yes, and..." or "Yes, but..." Similar to scientific discovery, the best answers should create more questions. A simple "yes" brings a sense of closure to that situation, and while the reader might be satisfied in bringing that story arc to its conclusion, it takes away that drive to continue reading just one more page, one more chapter.
Think about this: For anything we read, any play or movie we watch, we should have some form of engagement with the story. At any point, there should be at least one question in our head. If there isn't, then why are we going through the entire process of reading the book or watching the play? Our engagement should be one of discovery. We should feel invested; we should want to move and grow with the narrative and the characters. Even during the scenes that tie one act to the next, we still need to wonder what is going on. If there isn't, then why are we a part of this?
It may sound like an exaggeration, but as writers, we should want our reader to feel compelled to read our work from cover to cover in one sitting. The reader should be hooked, dragged in. They should never want to put it down. They should always be telling themselves, "I just want to see how they find their way to the 95th Street bridge, and then I'll go to sleep." Of course, two hours later, the characters are long past 95th Street but the reader is saying, "I'll just read until they remember where they left the briefcase." And so it goes.
This is asking a lot from any reader, but underneath it all, the principle is the same. We always want our readers to be engaged, and it is our responsibility to make sure a few unknowns still linger even when a major plot arc is concluded. When a chapter gives a big reveal, and the reader asks, "So she is his long-lost sister?", the answer should be, "Yes, but..." The reader has an answer, yet wants to go further.
Some writers might challenge the importance of this. They may ask, "Isn't this just teasing the reader? Can stories be written without relying on this technique? Wouldn't it be easier to tell the story without all these games?"
I will always answer, "Yes, but..."