It is simply a fact that some people long to travel the entire world, and do not flinch from nights in wild forests or from the heat of the desert or from the anger of a tempest. It is simply a fact that some men long to climb the loftiest of mountains, others to explore the harshness of Antarctica, others still to circumnavigate the world in hot-air balloons. Why do they do it? For the challenge, we are expected to believe. And the newspapers and the journalists will not shut up about these people. But there are other, more modest people, whom for the most part the journalists avoid, who are frightened to step out into a street. It is a fact that it is too challenging for them. They cannot do it. This latter group of people, who almost always exist in solitude, are so panicked by the world that they close themselves up inside houses, inside rooms, and never leave again. The longer they stay inside the harder it is for them to peer out; they may be brave enough at first to touch door handles but very soon it will be impossible for them to turn them.
--from Alva & Irva: The Twins Who Saved a City, Edward Carey