Question about the movie "Cast away" with Tom Hanks?

What exactly did "Wilson" (the ball) represent in this movie ?

1. The fears of a human being
2. The longed freedom of any human being
3. The longed mistress
4. Or what ?
Update: Cel !! ROFLMAO ! As usual, your directness and empathy astonished me !
Update 2: Grazie Ivanino !
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