Nothing is so difficult as not deceiving oneself. - Ludwig Wittgenstein
A cognitive bias is a systematic pattern of deviation from norm or rationality in judgment. Individuals create their own "subjective reality" from their perception of the input. An individual's construction of reality, not the objective input, may dictate their behavior in the world. Thus, cognitive biases may sometimes lead to perceptual distortion, inaccurate judgment, illogical interpretation, or what is broadly called irrationality.
Although it may seem like such misperceptions would be aberrations, biases can help humans find commonalities and shortcuts to assist in the navigation of common situations in life.
The film Perspective demonstrates how easily cognition can be distorted and become biased. Acknowledging our own biases is challenging, and it is easy to revert back to what other people think.
Humans are social animals. Not wanting to be vulnerable, everyone desires to fit in. In homogeneous societies, being silent is strongly encouraged as opposed to asking critical questions. These invisible rules apply to both the private and public spheres.
Reference: Haselton MG, Nettle D, Andrews PW (2005). "The evolution of cognitive bias." / Kahneman D, Tversky A (1972). "Subjective probability: A judgment of representativeness"/Baron J (2007). Thinking and Deciding / Ariely D (2008). Predictably Irrational: The Hidden Forces That Shape Our Decisions.