I cannot speak for everyone, but I think the reason why certain people use entertainment for emotional completion, is because it helps to fill some form of void that they have in their lives. The lyrics of a song might strongly resonate with your own feeling of pain after a rejection, a movie character could experience situations that you have in the real world - scene for scene - so they become very relatable, a group of friends in a sitcom might mirror your own ideal image of a friend circle. Fictional entertainment can allow a person to live out a fantasy of being somebody, or doing something, that they cannot realistically achieve in the real world.