I have a lawsuit which in part hinges upon cognitive bias. I found this short section from Never Split the Difference, to be a particularly clear and succinct explanation of the process:
Through decades of research with Tversky, Kahneman proved that humans all suffer from Cognitive Bias, that is, unconscious—and irrational—brain processes that literally distort the way we see the world. Kahneman and Tversky discovered more than 150 of them. There’s the Framing Effect, which demonstrates that people respond differently to the same choice depending on how it is framed (people place greater value on moving from 90 percent to 100 percent—high probability to certainty—than from 45 percent to 55 percent, even though they’re both ten percentage points). Prospect Theory explains why we take unwarranted risks in the face of uncertain losses. And the most famous is Loss Aversion, which shows how people are statistically more likely to act to avert a loss than to achieve an equal gain. Kahneman later codified his research in the 2011 bestseller Thinking, Fast and Slow.3 Man, he wrote, has two systems of thought: System 1, our animal mind, is fast, instinctive, and emotional; System 2 is slow, deliberative, and logical. And System 1 is far more influential. In fact, it guides and steers our rational thoughts. System 1’s inchoate beliefs, feelings, and impressions are the main sources of the explicit beliefs and deliberate choices of System 2. They’re the spring that feeds the river. We react emotionally (System 1) to a suggestion or question. Then that System 1 reaction informs and in effect creates the System 2 answer.
Voss, Chris; Raz, Tahl. Never Split the Difference: Negotiating As If Your Life Depended On It (p. 12). HarperCollins. Kindle Edition.