Raw genius is often required to intuit the hidden connections between an established mathematical truth and an unsuspected result, and arrogant self-confidence to undertake the formal proof. But the disturbing implication of A Beautiful Mind, a masterful biography of the Nobel Prize-winning mathematician John Nash, is that these same qualities may leave their holders unusually prone to mental illness-especially the mysterious disorder known as paranoid schizophrenia. Unchecked insight detects hidden connections everywhere, Nash's case suggests, and unchecked egotism spawns grandiose delusions.

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