The hard–easy effect is a cognitive bias where individuals overestimate success in difficult tasks and underestimate it in easy ones. It is typically identified via calibration curves, where subjective confidence is plotted against the actual proportion of correct responses.

The sources explore this phenomenon across diverse domains: animal learning (including brightness, auditory, and flavor discrimination in rats and pigeons), human cognitive tasks (mental arithmetic, general knowledge, and memory review), and complex decision-making under acute stress. These materials evaluate competing interpretations, such as selective attention, stimulus generalisation, and ecological models.

Final learnings highlight the ubiquity of the effect, which manifests across various sensory modalities and regardless of individual judge types. In animal psychology, progressive training (transitioning from easy to hard versions of a task) often facilitates learning more effectively than training on hard tasks alone. In human contexts, acute stress and time pressure significantly impair decision quality, leading to higher error rates even at lower complexity levels. Methodologically, some sources suggest the effect might be a statistical artifact resulting from scale-end effects, linear dependency, or biased item selection in experiments. However, other studies maintain that it is a robust indicator of how miscalibrated confidence impacts performance and self-regulated learning. Ultimately, the subject illustrates the complex interplay between perceived difficulty, actual accuracy, and environmental context.

The halo effect is defined as a cognitive bias where a positive overall impression of an entity, such as a person, company, or brand, influences one’s feelings or opinions about that entity in unrelated areas. It is essentially the inability to evaluate individual attributes separately from a general impression, leading to trait ratings that are more highly intercorrelated than objective measurement would reveal. This concept was formally coined by Edward Thorndike in 1920.

Research spanning various fields has confirmed and explored this bias:

• Foundational Psychology: Early research by Sheldon J. Lachman and Alan R. Bass utilized a direct method correlating general liking with specific trait ratings, finding stronger correlations (.60 and .76) when initial general liking was extreme. Learning from sources suggests the effect is pervasive, though training can lead to more analytical judgments and reduce the halo error. However, the effect is robust and not easily mitigated, even when individuals are forewarned about it.
• Corporate and Marketing: The halo effect influences consumer brand attitudes, especially when product familiarity is low. In corporate crisis management, a favorable prior reputation can act as a “shield” against reputational damage, though this benefit is often limited to organisations with very favorable reputations. Similarly, Corporate Social Responsibility (CSR) activities can generate a positive halo, acting as a buffer against negative publicity, particularly when the CSR activity is highly congruent with the company's image. One study found that higher CSR scores led to $2 million less in fines for Foreign Corrupt Practices Act violations, demonstrating the effect on prosecutors who are susceptible to a general positive image.
• Evaluation and Perception: The "attractiveness halo effect" shows that physical attractiveness can lead to inflated ratings of unrelated positive characteristics like intelligence or competence. In management accounting, objective performance can create a halo effect that mediates perceived employee morality, influencing subjective decisions like ex-post bonus reductions following misconduct. This bias can be reduced when managers are prompted to provide justification for their decisions, increasing accountability and deliberative thought.
• Healthcare: Hospitals benefit from a halo effect of hospitality, as patients weigh room and board aspects (like nurse communication and quiet rooms) more heavily than objective medical quality or patient survival rates when determining satisfaction. This is because hospitality serves as a visible proxy for hard-to-observe medical quality.

Attribution errors are cognitive biases that systematically affect how individuals explain the causes of behaviour and events, often leading to inaccurate or unjust assessments. The most foundational of these is the Fundamental Attribution Error (FAE), also referred to as the correspondence bias, which is the tendency to overemphasize dispositional or personality-based explanations for others’ behaviours while simultaneously underestimating the impact of situational factors. Lee Ross coined this term in 1977.

Research has consistently demonstrated the FAE, notably in the seminal Quiz-Bowl Study (Ross, Amabile, and Steinmetz, 1977), where contestants and observers overestimated the questioner's general knowledge due to the advantage conferred by their role. Other attribution errors include the Self-Serving Bias, Actor-Observer Bias, and the Ultimate Attribution Error (UAE), which applies FAE across entire groups. Studies investigating UAE in Indian university students, however, found evidence that inter-group attribution bias may not be universal, suggesting that higher education influences these social cognition processes.

Learnings from attribution research reveal that these biases are not universal but are influenced by culture and age. For instance, individualistic cultures are generally more prone to FAE than collectivist cultures. In organizational theory, the Theory X management style is proposed to have arisen from managers committing the FAE, attributing workers’ perceived lack of motivation to laziness (disposition) rather than highly restrictive and unmotivating work situations. Lee Ross later highlighted a broader cognitive bias called Naïve Realism or the “Truly Fundamental Attribution Error”: the conviction that one’s own views are objective, leading to the attribution that opponents who disagree are biased or irrational. To mitigate these errors, strategies include increasing self-awareness of biases, promoting critical thinking to question assumptions, and practicing perspective-taking to consider situational factors influencing others' actions. Technology and social media, which encourage instantaneous judgments based on limited context, necessitate increased media literacy to combat attribution errors in the digital age.

Functional fixedness is a cognitive bias originating in Gestalt psychology, defined as the inability to repurpose an object for any use other than its original or traditional function, thereby negatively impacting problem solving when a novel use is required. Misleading functional knowledge is considered to be at the core of this bias.

Seminal research, beginning with Duncker's Candle Box problem, established functional fixedness as a key psychological phenomenon. Modern studies have explored its mechanisms using experimental groups differentiated by learning modality: Reading (R), Video (V), or Manual (M) instruction. Further investigations examined its universality in a technologically sparse culture (the Shuar), and modality effects (pictures vs. words) in creative tasks like the Alternative Uses Task (AU task).

Findings suggest that functional fixedness occurs regardless of the learning modality employed, as long as misleading functional information is provided. The bias is generally limited to simpler problems and often dissipates after the first failure. Crucially, individual differences such as better intuitive physics knowledge and fine motor skills were identified as protective factors against the bias. Research indicates that functional fixedness is a universal cognitive architecture, present even in non-industrialised cultures. Moreover, stimuli presented in pictorial format tend to induce fixedness more strongly than verbal stimuli in creative thinking tasks, by priming abstract knowledge related to normative function. Strategies for overcoming FF include abstracting design decisions ("uncommitting") and systematically breaking down an object into generic parts defined by shape and material, thus decoupling function from form.

The Frequency Illusion, also known as the Baader-Meinhof phenomenon, is a cognitive bias wherein a person notices a specific concept, word, or item far more frequently shortly after recently becoming aware of it. This illusion is not due to an objective increase in the phenomenon, but rather a result of heightened awareness. It operates through two primary psychological processes: selective attention, which focuses the brain on relevant stimuli, and confirmation bias, which reinforces the perception by leading individuals to notice evidence that supports their hypothesis while disregarding contradictory information.

Linguist Arnold Zwicky coined the term "frequency illusion" in 2005, highlighting that professional linguists and ordinary people are susceptible to it. Research has been conducted across various domains to study this effect and its mechanisms. For instance, Zwicky noted the exaggerated perception of quotative 'all' usage among young speakers; transcription analysis showed its actual frequency was very low. Separately, studies investigated the related illusory truth effect, finding that repeating trivia statements up to 27 times increased their perceived truthfulness. A computational, agent-based model examined confirmation bias in a signal detection task, where agents detected A or B signals, with their bias determined by the first signal successfully detected.

The research yields several key learnings: in the agent model, biased agents generally outperformed unbiased agents when signal environments were imbalanced, suggesting confirmation bias can act as an advantageous heuristic by adjusting attention towards the most common type of data. Additionally, in the illusory truth research, increases in perceived truth were found to be logarithmic. The largest increase in perceived truth occurs after encountering a statement a second time, with subsequent repetitions leading to progressively smaller increases that may eventually lose practical impact. This evidence demonstrates that while initial intuitions (like those leading to the frequency illusion) can be a starting point for research, they must be rigorously tested, as subjective experience often leads to misapprehensions about actual frequency.

The empathy gap is a psychological bias where individuals struggle to accurately predict or understand the emotions and behaviors of others, or their own future selves, when in different emotional or visceral states. It is often defined as the hot-cold empathy gap, which contrasts states influenced by intense emotions like anger, pain, or hunger ("hot") with calm, rational states ("cold").

Research highlights several manifestations:

• Hot-cold gaps impact medical decisions, with patients in a "hot" state of distress (e.g., after a cancer diagnosis) making treatment choices they might reconsider when calmer. Smokers in a "cold" state also underpredict future cravings.
• Egocentric empathy gaps cause individuals to misestimate others' valuations in contexts like buying and selling, leading to financial losses and misattributions of greed.
• Empathy gaps for social pain demonstrate that those not actively experiencing suffering (e.g., bullying, ostracism) underestimate its severity for others and their past selves, impacting support for victims and policy responses.
• AI's empathy gap refers to conversational AI's failure to respond adequately to complex human emotions, especially in children, due to limitations in natural language processing and algorithmic bias, potentially producing harmful outputs.

Major learnings indicate these gaps lead to poor personal and policy decisions, causing misunderstandings and missed connections. However, empathy is a teachable skill. Strategies to bridge the gap include: pausing before reacting, practicing emotional self-regulation, and labeling emotions. Considering similar situations can also reduce affective distance and improve judgments.

Effort justification is a psychological phenomenon where individuals enhance the perceived value of an achievement or outcome after investing significant effort, trouble, or pain to obtain it. This concept is deeply rooted in cognitive dissonance theory, pioneered by Leon Festinger (1957), which posits that individuals are motivated to reduce psychological discomfort arising from inconsistencies between their beliefs and actions. In this context, justifying strenuous effort for an outcome that might objectively be underwhelming serves to restore cognitive consistency.

Classic research demonstrating effort justification includes Aronson and Mills's (1959) study, where participants who underwent a severe initiation to join an unexpectedly dull discussion group subsequently rated the group as significantly more appealing. Festinger and Carlsmith (1959) also found that subjects who were paid a small reward to lie about a boring task later rated the task as more enjoyable than those given a larger reward, thus justifying their insufficient external incentive. In a therapeutic context, a study on weight loss by Axsom and Cooper (1985) showed that subjects who engaged in high-effort tasks experienced greater and more sustained weight loss compared to low-effort or control groups, suggesting that the effort enhanced the perceived value of the weight loss goal. Furthermore, studies with adult humans and children have revealed similar effects in asocial contexts, where increased effort or delay led to a preference for associated stimuli.

Interestingly, justification of effort effects have also been observed in non-human animals such as pigeons, starlings, mice, rats, and even grasshoppers. For these animal findings, and as an alternative explanation for some human results, a non-cognitive mechanism known as "within-trial contrast" has been proposed. This model suggests that a relatively aversive event (e.g., high effort, a long delay, or the absence of reinforcement) experienced prior to an outcome can enhance the perceived value of that outcome through a perceptual contrast effect.

Key learnings suggest that while effort justification can positively motivate individuals and lead to increased commitment, it can also lead to irrational decisions, an escalation of commitment to failing projects, and distorted critical thinking by overvaluing outcomes based on expended effort rather than objective merit. To mitigate these potential negative impacts, strategies such as practicing mindfulness, embracing failure, seeking external perspectives, and applying critical thinking are recommended. Conversely, research also highlights that effort can inherently add value, not just to the product of effort, but to the effort itself, becoming intrinsically rewarding.

The denomination effect is a cognitive bias where individuals are less likely to spend money in large bills compared to an equivalent amount in smaller denominations or coins. Larger bills are often overvalued, acting as a self-control mechanism to deter spending, as people are reluctant to "break" them and lose track. Smaller units are undervalued and spent readily.

Priya Raghubir and Joydeep Srivastava's (2009) foundational research demonstrated less spending from a single $5 bill than from five $1 notes. Large denominations are perceived as less fungible, serving as a pre-commitment strategy to save. If this self-control fails, a "what-the-hell" effect can lead to increased spending. Smaller denominations are also harder to monitor and recall, contributing to easier spending.

Recent studies introduce important nuances:

• The "denomination-tipping effect" (Zenkić et al., 2023) reveals a reversal in social contexts; embarrassment makes consumers less likely to tip smaller denominations.
• The "denomination–spending matching effect" (Li & Pandelaere, 2021) suggests consumers prefer denominations that match the purchase price (small for small, large for large), driven by "denomination fit" that boosts satisfaction.

Practical applications include retailers using smaller change to encourage purchases and consumers carrying mismatched denominations to curb spending. Investors should evaluate a company's holistic value rather than just share price to avoid this bias.