The city in which Lina lives and works is the only place left in the world that has electricity. Outside of the controlled space of Ember, it is completely dark. Due to the dark and potential danger, the citizens of Ember never leave the confines of their city.
All it would take was the courage to walk away from Ember and into the darkness, and then to keep going.
This quote was said by Lina at one of the times she was talking to her friend Clary. Lina came to understand that Ember is in danger of extinction if someone does not figure out a way to repair the generator of the city. Lina wants to help her city, but she has responsibilities to her grandmother and her little sister as well as her job as a messenger. Leaving Ember would mean going out into the dark, unknown and unprotected world where she would have no information about what to expect or how to protect herself. In spite of all these concerns, that’s what she is determined to do. Lina was very brave in taking the risks she felt were necessary to try to preserve the life of Ember and its citizens.