Answer:
In Robert Heinlein's novel, "Starship Troopers," the main character, Johnny Rico, decides to join the Mobile Infantry because he wants to prove himself. He feels like he has something to prove to himself and to his family, and he thinks that joining the Mobile Infantry is the best way to do that. He also wants to serve his country and believes that being a member of the Mobile Infantry is the best way to do that. So, there are several reasons why Johnny Rico decides to join the Mobile Infantry, but they all come down to his desire to prove himself and serve his country.
