Cognitive biases are systematic patterns of deviation from rationality that influence how people perceive, judge, remember, and decide. Rather than occasional mistakes, they are predictable tendencies built into the architecture of human cognition. Kahneman's distinction between System 1 (fast, automatic, intuitive, emotional) and System 2 (slow, deliberate, analytical) is the most influential framework for understanding why biases exist: most daily thinking is performed by System 1 because it is cheaper and usually accurate enough, while System 2 only steps in when something triggers hesitation or effortful review. This means that bias is not a sign of stupidity but the natural output of an efficient mind working with limited information and finite time.
Several meta-biases explain why biases are hard to escape even when known. The bias blind spot is the tendency to recognize biases in others while believing oneself relatively unbiased. Naive realism takes this further: many people believe they see the world objectively and that disagreement comes from others' ignorance or bias. The WYSIATI principle ("What You See Is All There Is") captures how System 1 confidently builds coherent stories using only the information currently in mind, ignoring what is absent. Because of these recursive effects, simply learning about biases rarely eliminates them; this is the deepest practical takeaway of the literature. Knowledge is necessary but not sufficient.
A further reason biases persist is that many of them once served adaptive purposes or remain accurate enough in the ancestral environments in which they evolved. Loss aversion, for example, can be understood as a sensible risk-management response to asymmetric consequences. The goal of debiasing is therefore not to eliminate intuition but to design conditions under which slower, more deliberate cognition can check fast judgments. As the deck's closing summary puts it: systematic processes work better than willpower.