A cognitive bias is a systematic deviation in judgment: a mental shortcut that leads us to perceive, decide, or remember incorrectly, without us even realizing it.
The foundational framework comes from Daniel Kahneman and Amos Tversky, whose pioneering work on heuristics and biases (1970s), synthesized in Thinking, Fast and Slow (2011), distinguishes two modes of thought: a fast, intuitive, and automatic System 1, and a slow, analytical, and effortful System 2. Most of our decisions rely on System 1—meaning shortcuts, which naturally lead to biases such as anchoring, confirmation, availability, and loss aversion.
For design, this knowledge is a double-edged sword. On one hand, it helps craft interfaces that reduce cognitive load and beautifully guide decision-making—exemplified by Thaler and Sunstein's nudge (Nudge, 2008), like a brilliantly set default choice or a perfectly timed piece of information. On the other hand, those exact same levers can be used to exploit these biases against the user, such as artificial urgency, simulated scarcity, or deceptive anchoring. It is indeed a fine line between empowering and exploiting.
And there is a second, more subtle trap: designers have their own biases! Confirmation bias leads us to see exactly what we hoped for in a user test; the halo effect makes us overestimate a sleek, seductive idea. Simply knowing user biases is not enough; we must also stay mindful of our own.
Our driving principle: leverage the science of biases to simplify decision-making for the user, never to compromise their free will. A thoughtful default choice helps; a deceptive one betrays trust. Regarding methodology, we counter the designer's personal biases with the ultimate antidote: real-world user testing, embracing the possibility of being proven wrong.
Related concepts in play: cognition, attention, dark patterns (the exploitation of biases), data-driven design (biases in interpreting metrics), and affordance.
References: D. Kahneman & A. Tversky, heuristics and biases; D. Kahneman, Thinking, Fast and Slow (2011); R. Thaler & C. Sunstein, Nudge (2008).
Rémi
Gréau
Director of Design
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