Perchance to Dream by Sigmund Freud
Until Sigmund Freud's The Interpretation of Dreams appeared in 1900, dreams were considered either to belong to the realm of mysticism and superstition, or were the object of unscientific "dream books" that told the reader what the dream meant. After the publication of what must be considered Freud's most important book, dreams were taken seriously in psychotherapy. Today, whatever the school of therapy, it would be rare not to give dreams some significance. This is entirely due to Freud, who called dreams "the royal road to the unconscious."
Freud used this book to reveal much of his inner life. This required courage, and encouraged others to take the same route. Even if we reject Freud's interpretations of his own dreams, or find them lacking in scientific rigour, we cannot fail to admire them as remarkable literary achievements. Probably no other author, ever, has subjected his or her own dreams to such merciless investigation.