Symbolism, Imagery, Allegory
If you're like us, then you're probably wondering what's up with William's "temporary blindness induced by trauma." At first we have no reason to question whether the guy is blind or not—he's wearing dark glasses, and he looks the wrong way when waving goodbye to Flora. Plus, what would be the point of pretending you're blind?
As the story goes on, though, and his aunt says he's not actually blind, we become curious about what's happening in that brain of William's. Eventually, he spells it out for us:
"My name is William. William. William Spiver. Not Billy. I was Billy one time too many. I cracked. I pushed Tyrone's truck into the sinkhole, and when my mother found out, she was incandescent with rage. I looked upon her rage, and you know what happened then. I was blinded by disbelief and sorrow." (61.26)
In other words, William went blind after his mom kicked him out for hurting her new husband's truck. He literally stopped seeing as a way of handling the terrible truths underlying his mom's behavior (you know, like that she loves her new husband more than her son). It's clear that William has a lot of feelings about his mom's decision, and hasn't quite worked them all out when we first meet him.
By the end, though, William gains his sight back, but only after he learns to talk about the incident. Coincidence? We think not. Not talking about what happened to him only adds to William's trauma, so he's got to let it all out in order to get better. He thinks he's avoiding looking at it by keeping it inside, but what's happening instead is he's haunted by the pain. He's got to face what's happened in order to move on.
In the end, William's sight is a symbol for what he is feeling inside. So when he's blinded to the world around him, he's in a dark and empty space emotionally. He only sees again once he starts to deal with his mother's betrayal of him, which is at least partly thanks to becoming friends with Flora.