I'm of the firm belief that a writer's subconscious is busy planting things the writer is blind to at the moment.
When I rework a novel, I'll find lots of foreshadowing of events I didn't think I'd planned until the moment I wrote it, and I'll discover that certain types of metaphors or images keep appearing that fit a theme or event I didn't know was coming.
Part of the trick for a writer is going back over your work and building on the bread crumb hints left by your subconscious. Make it obvious enough that the reader’s subconscious also picks up these crumbs to create more resonance in the novel.
NOTE: My subconscious just showed its unhappiness of my comments by making me unable to spell "subconscious" which is a word I normally spell with ease.