/lit/ - Literature

Hey /lit/

Are there any tips in helping a reader remember a specific thing earlier on in a novel? How do you tell a reader to remember this scene/line/description because it's relevant later in the story?

To be more specific:

I've got a riddle at let's say 5% in of a novel, the main character believes he's solved it, and it isn't mentioned again until ~80% in, when it's solved. The riddle is told and 'solved' in maybe 50 words max. How can I emphasize the fact that it's important early on, especially when I practically discard it?