By all means, when your book is over, have a solid conclusion that neatly wraps up all of the loose ends of that book. If there are a few loose ends or teasers for another book, by all means leave them open, but the story you are writing should be able to stand alone as a solid and complete one. What I mean when I say stop answering everything is this: Show don’t tell.
If the setting is a post-apocalyptic future, we don’t really need to know every detail of how it came to be that way. If it is a horror, we don’t really need to understand everything about how the threatening ‘whatever it is’ came to be. We don’t need someone giving us exposition about the exact nature of the cure unless that is intricately tied to the plot. We don’t need to know why the boy likes the girl more than anyone else. Or rather, we don’t need to have these things stated to us.
What is needed instead is to have contextual information placed into the setting and scenes that give us the ability to come to these conclusions on our own. An old newspaper headline in the first example might be ten times more powerful than our hero talking to himself for three pages. Just an example.
It would seem like something well known by now, yet every day writers find someone reminding them of this. Even professional authors fall prey to it, though editors are good at guiding them back away from it again more often than not. Is it vital to your stories conclusion for the information to be fully understood and every question answered? If the answer is no, then by god stop giving all the answers. Just give them all of the hints needed to work it out on their own if they care and pepper them among the pages.
Answering all of my questions may leave me without any loose ends, but it is also not particularly compelling. It doesn’t draw my imagination out of its shell and induce it to flex some brawn. It doesn’t challenge me, but instead assumes I am simple minded and need my problems solved for me. Give me substance. Show, don’t tell.