Question

Cause readers to brood over the resolution of the story and causes readers to search out its implications to get more from it.

Answer 1

I believe that an unhappy ending can do that. 
When a story has a happy ending, then you finish it and you feel satisfied and joyful about how the story ended. On the other hand, if the story ends in an unhappy manner, you start thinking about the resolutions and imagining what could lead to such an ending and how it could be fixed.