What a great thread!
The book that changed my life is, without doubt,
Joseph Heller's Catch 22.
Slaughterhouse 5 by
Kurt Vonnegut is also strangely compelling. So it goes...
The Prehistory of the Mind by
Steven Mithen opened my eyes to the evolution of human consciousness whilst
An Anatomy of Thought by
Ian Glynn was wonderfully illuminating on how the brain really works.
Great books.
Though Catch 22 is definitely head and shoulders above the rest for its effect upon my (then) young mind...
Mr Mephisto