We often praise the importance of rational analysis, believing that people should be a little more rational and not be swayed by emotion or unnecessary information. Yet if being rational means objectively analysing all the available data and arriving at the best possible decision, most human beings would be classed as irrational — and the reason is precisely the cognitive biases that influence us without our ever noticing.
Cognitive Bias and Rationality
The best way to explain cognitive bias and human irrationality is through examples.
Suppose you want to buy a can of coffee. The supermarket downstairs charges HK$20, while a grocery shop at the far end of the street charges only HK$3. Would you be willing to walk 15 minutes to the distant grocery shop? Quite possibly you would. Now suppose you want to buy a mobile phone. The electronics shop downstairs charges HK$5,888, while a department store at the end of the street charges HK$5,871. Would you still be willing to walk 15 minutes to the department store? You might hesitate, and in the end decide to buy the phone you need at the shop downstairs. The saving is HK$17 in both cases, and the walk is 15 minutes in both cases — so why would people make different decisions and behave differently?
Economists have found that the same value — HK$17 — carries a different subjective utility in people's minds. Subjective utility falls as the objective value of an item rises. Not clear yet? Take a look at the diagram below.

Because subjective utility falls as objective value rises, the same HK$17 gap feels different to us depending on the value of the item. HK$17 is negligible against a phone costing more than five thousand dollars, but against a can of coffee it amounts to an 85% difference! You might insist that your decision was based on percentages. And yet HK$17 is HK$17 in any situation, and in theory a perfectly rational decision-maker should make the same choice in both cases.
Of course, humans have more than one cognitive bias, and they are not confined to economic decisions. Among those widely applied in marketing are the decoy effect and the endowment effect, which we will not discuss here for reasons of space. People likewise rely too heavily on certain (even irrelevant) information when forming judgements — for instance, finding content more agreeable simply because it is set in an elegant typeface, or making faulty assumptions on the basis of certain existing labels. When other people's behaviour goes wrong, we tend to attribute their mistakes to personal failings; when we ourselves slip up, we tend to blame external, environmental factors. Psychologists call this asymmetry attribution bias.
Cognitive biases mostly show that people overestimate their own rationality, but our lives are hardly short of irrational moments either. Being controlled by emotion, acting on impulse — these are far from rare phenomena. As people deeply affected by them, how then should we regard them?
How Should We Regard Our Own Irrationality?
Whether absolute rationality is worth pursuing, I dare not presume to judge. But cognitive bias is not merely a weakness of human nature. According to the theory of evolutionary psychology, our mental processes have all been shaped by evolution and serve the survival of the organism. Cognitive biases often arise because people rely on certain heuristics, also known as mental shortcuts. People use these mental shortcuts to make decisions based on only a small amount of information. Since we have to make countless decisions every day, carefully calculating each one would demand enormous mental resources and time. In most situations, even though mental shortcuts are sweeping generalisations, they still allow people to reach correct decisions — though not necessarily the most correct ones. In an environment of competition and survival of the fittest, saving resources and time may matter more than making the most correct, fully rational choice.
The role of emotion in decision-making should not be overlooked either. The neuroscientist Antonio Damasio once took on a case: a patient named Elliot whose cognitive abilities appeared, on the surface, to be intact — he could rationally analyse the consequences of different choices, yet he had lost the capacity to feel emotion. When Elliot made decisions, although he reasoned rationally, he was unable to actually decide; Damasio traced the cause to his lack of feeling. This case led Damasio to later propose the Somatic Marker Hypothesis, which holds that when making a decision a person needs to imagine the feelings that will follow it, and to draw on the bodily reactions those feelings trigger, in order to judge the value of different choices and decide how to handle matters big and small in life. This shows that emotion is indispensable to human decision-making.
Although human behaviour is not like a rational computer program, that is precisely where psychology becomes fascinating. TreeholeHK has now launched a Psychology 101 online course. As the saying goes, "Know yourself and know your enemy, and you will never be defeated." In every area of life — whether in your career or in love — understanding both yourself and the other person helps you find your way out of the fog and discover the direction in your heart. The course is taught by a psychology professor from a local university, and we hope it will help you understand yourself and your relationships through psychology, and see your own life from a fuller perspective.









Comments3 comments
田中左木龍
$20 嘅咖啡 可能每日都要買
$5,888 嘅電話 兩三年先買一次
明白呢個例子嘅比較~
只係實際操作上有更多其他考量
JOE
情感可能本身可能是理性的。我們認為情感不理性,可能只是因為真正的理性,不是我們理解的理性。
最近我看了一本書,叫道德部落,作者指出,幾個群體之中,大家都非常道德,但當幾個道德群體一起,出現了碰撞,慢慢演變成戰爭,作者指這是「常識型道德悲劇」
例如像是香港與中國大陸在2019年事件,或者中美冷戰等,也可以是一種「常識型道德悲劇」
作者認為,道德,背後其實係一種「合作機制」,目的是為了讓大家更多合作,更少磨擦,提高大家的存活率,促進和諧,減少矛盾紛爭與悲劇。
但是,大自然演化規律係,人類道德係利我群,但不是為了利「他群」或「世界大同」存在。所以會有一些「利我群」,但「不利自己」、「不利他群」、又不利「世界大同」的「非理性行為」。
另外,作者認為,友誼真正原因係基於合作。
如果我們了解友誼是基於合作,可以解釋到友誼之間的矛盾,包括非理性矛盾。
例如辯論或面對爭議,兩個喜歡學術研究的人一齊爭議辯論,好大可能會加強雙方間的友誼,因為真理往往越辯越明,辯證法好有用。
但如果係一個重視實務的人,對於辯論或爭議,會變得不耐煩,更可能會「撕裂」大家的友誼,因為你做project要做得好,最緊要係大家有共識。
JOE
另外,人腦的運算,應該係像CHATGPT一樣,基於連結義、大數據統計與機率學習,而非像傳統程式的演算法,或If then Else 規則運作。所以不同的人,如果他所接觸的東西或讀到的東西不同,便有不同的性格、情緒和思想。而傳統對理性的定義基本都係基於假設,並非實證。
我看一些講談判的書籍也有提到,情緒可能是一種「看似不理性」的「理性策略」。
當然,在神經生物學與分子細胞生物學角度看,如果一個人的腦部受了傷,會令情緒失控,即情緒病。此時候,藥物或手術可能會有幫助,但如果醫師誤疹、或手術做得不好、或開錯藥,會有反效果。