The source of his amazing powers seems to be that of screenwriting convenience.
The only plus I would grant the movie is seeing the origin tale of Bilbo and the schizophrenic creature Gollum brought to life. This at least gives the movie its few moments of interesting vitality -- two hours in. Yawn. After that, the film ends essentially where the action of any other movie would begin to pick up momentum. And at this, Bilbo looks to the distance and delivers the ironically appropriate final line, “I believe the worst is behind us.”
God, I hope so.