Each elder or sister spends every moment of every day in tandem with another, sleeping and rising at the same time in a shared room. That companion isn't always American and doesn't necessarily speak English. For the next two years, these "companionships" proselytize for 10 hours a day, six days a week, knocking on doors and offering The Book of Mormon to strangers, often in languages the missionaries barely know how to speak. They must persuade people to listen and learn to persevere in the face of near-constant rejection. "I don't think there's any more demanding profession than being a Mormon missionary," says Christensen.