One of the most, if not the most, iconic parts of "Cast Away" is Chuck's relationship with Wilson, the volleyball named after Wilson Sporting Goods, the company the ball originates from. Wilson, which is stained with Chuck's bloody handprint and given a smiley face, provides Chuck with his only source of companionship during his time on the island.
Chuck's relationship with the ball evolves into full-blown bursts of emotional back-and-forth with the inanimate object. It sounds silly in concept (especially if all you've seen are parodies of the movie), but thanks to Tom Hanks' dedicated performance, we're taken on as much of an emotional roller coaster as he is.
This is most evident in how their relationship concludes. Chuck manages to build a durable raft, using the plastic from a portable toilet that washes up to the island as a sail. He successfully escapes and gets out into the open ocean, but after a harsh storm, Wilson falls off the boat and floats away, leaving Chuck emotionally shattered.
Chuck's journey sees him start off as an obsessive workaholic overly concerned with time and become a humbled individual, stripped of the feeling of control he had over his life. With this in mind, Wilson can be seen as the last shred of Chuck's hubris, an entity of his own creation with a literal part of him plastered onto it, floating away. His desperation to hold on to Wilson is not only for friendship but also for stability and a sliver of what he considers normal. Wilson's loss is therefore a necessary component if Chuck is to complete his metamorphosis.
