Once a guy stood all day shaking bugs from his hair. The doctor told him there were no bugs in his hair. After he had taken a shower for eight hours, standing under hot water hour after hour suffering the pain of the bugs, he got out and dried himself, and he still had bugs in his hair; in fact, he had bugs all over him. A month later he had bugs in his lungs.
Having nothing else to do or think about, he began to work out theoretically the life cycle of the bugs, and, with the aid of the _Britannica_, try to determine specifically which bugs they were. They now filled his house. He read about many different kinds and finally noticed bugs outdoors, so he concluded they were aphids. After that decision came to his mind it never changed, no matter what other people told him . . . like "Aphids don't bite people."
A Scanner Darkly
Phillip K. Dick