For those who were confused/disappointed over the third act
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I think its the best part of the movie ,specifically because we get to know that the music or performing tours wasn't the real aim of both ruben and lou. Ruben himself lives a noisy life living all over america with his mom and his dad was never there for him.We get to know that lou had family problems and her dad keeps repeating that ruben was her 'refuge' of sorts,it is repeated again when they both have their final exchanges where they say 'you saved my life' to each other.The music/relationship in one way was his drug.The movie brilliantly masks the central theme -ruben's and lou's relationship. After getting his hearing back his relationship is clearly distorted just like everything else around him. He finds inner peace when he finally gets over his disability . As joe puts it ,he is in his kingdom of heaven at the end,sitting.