This collage page from one of my journals uses art as a personal metaphor, one I put together for the beauty I find in writing. My computer is nowhere near as gorgeous as a peacock feather, but the feather represents both how I see and what I try to do with my writing instruments. Behind the feather is a torn fragment of a watercolor I painted that I wasn't happy with, to symbolize my vision of the story (and my eternal conflict trying to realize it.) The rough dark page is the world beyond my story; the audience I can't see, the void I want to fill.
Would you have known that if I hadn't explained it? Probably not. Does not knowing what the page means to me personally diminish your enjoyment of it? It could, but it doesn't have to. I think it depends on how you relate to symbolism and how often you engage your sense of wonder and curiosity.
It would be great to publish books as colorful and creative as my personal journals, but because everything I write as a novelist is published in black and white, words are my only medium. Metaphors are both paint and brush, mortar and brick, courier and message. Very often we respond on many levels to a story, and not all of them register right away, if at all. In an open mind, metaphors can gain access to many different levels.
Sometimes metaphors are intensely personal, and without shared experiences, can be inexplicable. For example, while trimming trees last weekend we accidentally made this preying mantis temporarily homeless. We moved the mantis out of harm's way to a smaller tree, and now every time I mention a mantis to my guy, he'll remember everything that happened when we saved this one. If I use the mantis as a metaphor while talking to my mom, she'll just think I'm talking about a bug.
Metaphors invoking very common shared experiences can be recycled so much that they morph into a cliche, and it's easy as pie, and like taking candy from a baby to overuse them. Creating your own personal metaphors means really thinking about how your story symbols relate to the experiences of others, and what sort of response they will invoke in readers who have a good working sense of wonder. Employ your senses (colors, sounds and tactile sensations are good metaphor building materials, as we all share the world on the same basic sensory level.)
See? Piece of cake.
Related Link: Literary zone.com has a good post here defining different types of metaphors and gives some examples, if you're interested in reading up on them.