Thinking, Fast and Slow (Daniel Kahneman)
Daniel Kahneman's work in the psychology of belief and decision (much of it done in collaboration with Amos Tversky) has been central in shaping our understanding of human (ir)rationality in the 20th century.
In 2002, Kahneman was awarded a Nobel Prize— Tversky had died in 1996 — for having “integrated insights from psychology into economics, thereby laying the foundation for a new field of research.”
His work initiated what has been called the "biases and heuristics" tradition of research in cognitive science, which connects biases in reasoning with cognitive shortcuts (heuristics) that allow our reasoning to be fast and efficient, but which bypass our conscious, deliberative reasoning processes.
In this 2011 book, Kahneman gives a broad overview of his career and major developments in the field.
One of the central themes of the book is that we have two very different cognitive processing systems (System 1 ("fast") and System 2 ("slow")) which operate semi-independently of one another, and whose interaction can result in systematic errors of judgment. This dual-process framework has become a dominant model in contemporary research on human reasoning. The first chapters of the book are a good introduction to this framework.
The book is written for a general audience but it's a big book with a lot of content. I wouldn't call it an "easy" read, but because the ideas are so influential, I think it -- or a book like it -- belongs on every critical thinker's bookshelf.