The following quote is from p29 of Veronika Decides to Die (ISBN 0722540442) by Brazilian author Paulo Coelho.
It tells the story of a young woman who, after a failed suicide attempt, is admitted to a psychiatric hospital where she meets some curious and life-changing patients and medical staff.
Paulo Coelho was admitted to a psychiatric hospital himself when a student, and he drew on his own experiences to write the novel.
Veronika returned to her bed, and waited for the nurse to resume her reading. What did it mean to be mad? She hadn’t the slightest idea, because the word was used in a completely anarchic way: people would say, for example, that certain sportsmen were mad because they wanted to break records, or artists were mad, because they led such strange insecure lives, different from the lives of normal people. On the other hand, Veronika had seen thinly clad people walking the streets of Ljubljana in winter, pushing supermarket trolleys full of plastic bags and rags, and proclaiming the end of the world… What did it mean to be mad? Perhaps she should ask one of the mad.
Link to more info on the book.