Bob Fosse said that most songs fall into two categories: the "I Want" Song and the "I Am" Song. The "I Am" Song is, simply put, a song which establishes a character's personality, role in the plot, and/or motivations right away. It can be more effective than setting up a character by dialogue, and it's almost always more fun. Despite the name, the song doesn't have to be sung by the characters themselves. "The Villain Sucks" Song is an example of an "I Am" Song sung by other people about a villain they despise. May also be an I Am What I Am, but not always.