John Green said this quote

“ Why do writers use symbolism?” Okay, so let’s say you have a headache and you wanna tell someone about it and you say, “I have a headache!” and other people are like, “Yeah, whatever. Everybody gets headaches.” But your headache is not a regular headache, it’s a serious headache, so you say, “My brain is on fire!” to try to help these people understand that this is a headache that needs attention! That’s a metaphor, right? And you use it so that you can be understood. Now let’s say you want to take those same imagistic principles but apply them to a much more complex idea than having a headache, like, for instance, the yearning that one feels for one’s dreams. And you can see the dream but you can’t cross the bay to get to the green light that embodies your dream. And you want to talk about how socio-economic class in America is a barrier – a bay-like barrier, some would say – that stands between you and the green light and makes that gap unbridgeable. Now, you can just talk about that stuff directly, but when you talk about it symbolically, it becomes more powerful, because instead of being abstract it becomes kind of observable…. So I think that’s why. ”