Dick's stories typically focus on the fragile nature of what is real and the construction of personal identity. His stories often become surreal fantasies, as the main characters slowly discover that their everyday world is actually an illusion assembled by powerful external entities, such as the suspended animation in "Ubik", vast political conspiracies or the vicissitudes of an unreliable narrator. "All of his work starts with the basic assumption that there cannot be one, single, objective reality", writes science fiction author Charles Platt. "Everything is a matter of perception. The ground is liable to shift under your feet. A protagonist may find himself living out another person's dream, or he may enter a drug-induced state that actually makes better sense than the real world, or he may cross into a different universe completely."