Read the excerpt from The Time Traveler's Guide to Elizabethan England. There is no concept of "health and safety” in Elizabethan England, so you will inevitably feel vulnerable when you arrive. Nauseating smells and sights will assail your senses; contemporary standards of cleanliness will worry you. People die every day from unknown ailments, the young as often as the old. Infectious diseases periodically kill thousands within a few weeks. Even when plague is not in town, it lurks as an anxiety in the back of people’s minds and, when it does strike, their worry turns to terror. On top of the illnesses, the chances of being attacked and hurt are much higher than in the modern world, and workplace injuries are far more common. What is the central idea of this paragraph?