Heuristics are mental shortcuts (or rules of thumb) that aid our decision-making, judgements and problem-solving in everyday life. The concept was first introduced by Nobel laureate Herbert A. Simon and was later researched in depth by psychologists Amos Tversky and Nobel laureate Daniel Kahneman, famous for his book Thinking, Fast and Slow.
Since our mental computing power is limited, we developed heuristics allowing us to make decisions faster and more frugally than a rational analysis of all the information available. Many of these heuristics have developed over time such as the principle of expensive = good where price alone is the indicator of quality. The saying you get what you pay for saying further ingrains this in people. In addition, many brand leverage heuristics. For example, Tescos Finest might be a shortcut to quality, M&S Living Well might be a shortcut to health.
Heuristics work well most of the time, but, equally, heuristics can be sub-optimal and prone to error, leading to a variety of cognitive biases.