Phi Lý Trí (Predictably Irrational, Vietnamese edition)

Predictably Irrational, published in Vietnamese as Phi Lý Trí, is Dan Ariely's first major popular book and the work that established him as a leading public voice in behavioral economics. Its central argument runs directly against the classical economic assumption that people make decisions as rational, self-interested calculators: Ariely shows, through a long series of his own controlled experiments, that human irrationality isn't random noise around an otherwise rational baseline — it's systematic, predictable, and exploitable, which means it can also be studied, anticipated, and in some cases designed around.

The book moves through a sequence of specific, well-documented irrational patterns, each explored through Ariely's own experiments alongside real-world examples. Early chapters address the power of relativity in decision-making — how people judge value by comparison to available reference points rather than in absolute terms, which is why a strategically placed expensive "decoy" option can shift preferences toward a specific other choice. From there, Ariely examines the cost of "free," showing that zero-price offers trigger a disproportionate, sometimes irrational surge in demand compared to even very small positive prices, and explores how social norms and market norms operate on entirely different psychological logic — explaining why introducing payment into a previously favor-based relationship can backfire and reduce, rather than increase, willingness to help.

Later sections turn to self-control and procrastination, examining why people struggle to act in their own long-term interest even when they know better, and what kinds of structural commitments (deadlines, defaults, pre-commitment devices) actually help. The book also covers the influence of arousal and emotional state on decision-making, the surprisingly large effect of ownership on how people value what they already have, and how expectations themselves — before any product or experience is even encountered — can shape the actual subjective experience of it, not just the report of it afterward.

Throughout, Ariely's tone stays accessible and story-driven rather than academic, using vivid experimental setups (comparing magazine subscription options, testing how placebo pricing affects pain relief, observing how honesty shifts when cash is one step removed) to make abstract cognitive biases concrete and memorable. The book's broader implication, made explicit toward its close, is that once irrationality is understood as systematic rather than random, it becomes possible to design environments, policies, and personal habits that account for it — protecting against the biases that work against us and, more cynically, recognizing how markets and marketers already exploit the ones that work in their favor.