NISM-Series-X-B: Investment Adviser (Level 2) · Basics of Behavioural Finance

Introduction to Behavioural Finance for NISM Investment Adviser Level 2

Updated 11 October 2026 · Fact-checked

Behavioural finance studies how psychology affects the financial decisions of investors and the prices of markets. It challenges traditional finance, which assumes investors are fully rational. To solve exam questions, identify the assumption being tested (rational or not), match it to the right school of thought, and eliminate options with absolute words.

Understand Introduction to Behavioural Finance

Behavioural finance is the study of how real people make financial decisions. It combines finance with psychology. It asks why investors often act in ways that do not look logical, such as holding on to losing shares or following the crowd.

Traditional finance starts from a different view. It assumes investors are rational: they use all available information, process it correctly, and aim to maximise their wealth for a given level of risk. It also assumes markets are efficient, so prices reflect available information. In this view, any irrational trader is random and gets cancelled out.

Behavioural finance emerged because real-world evidence did not fit these assumptions. Investors were seen to trade too much, hold on to losers, chase recent winners, and follow herds. Markets showed bubbles and crashes that are hard to explain by rational behaviour alone. Researchers from psychology and economics began to explain these patterns using human limits and emotions.

Behavioural finance does not say investors are always foolish. It says people are "normal", not perfectly rational. They have limited attention, limited memory, and are influenced by emotion and by how choices are framed. Their errors can be systematic, meaning they repeat in a predictable direction, rather than random.

For an investment adviser, this matters in practice. Understanding a client's biases helps you give better advice, set realistic expectations, and avoid unsuitable recommendations. The scope covers individual investor behaviour (biases, heuristics, emotions), the way these affect market prices, and the practical use of this knowledge in advice.

Key formulas to remember

Traditional finance assumption: Investors are rational + markets are efficient; Rational means using all information correctly to maximise wealth for the risk taken.
Behavioural finance assumption: Investors are "normal" (bounded rational) + psychology affects decisions and prices; Errors can be systematic and predictable, not just random.
Two broad groups of behavioural errors: Cognitive errors (thinking/information processing) and emotional biases (feelings, impulse); Cognitive errors can often be reduced by better information or training. Emotional biases are harder to correct, so advisers often adapt the advice to them.

How to solve Introduction to Behavioural Finance questions

Use this method for any definition, comparison or scenario question on the introduction to behavioural finance.

1Read the question stem and decide what is being asked: a definition, a comparison, the reason for emergence, or a scenario.
2Look for the key assumption: is the investor described as rational and fully informed, or as influenced by emotion, habit or framing?
3If the stem says rational, utility-maximising or efficient, link it to traditional finance. If it mentions psychology, bias or irrational patterns, link it to behavioural finance.
4For a scenario, name the behaviour first (for example following the crowd or holding losers) and then place it in the right group.
5Cross out options with absolute words such as always, never or all investors, unless the stem demands them.
6Check that the chosen option does not claim behavioural finance says markets are always wrong or investors are always irrational.
7Choose the option that is most precise and consistent with the definition.

Quickest way: Rational or psychological: two-second test

When to use it: Use when you have little time on a definition or comparison MCQ.

Spot the trigger words: rational, efficient, maximise wealth means traditional finance.
Spot: psychology, bias, emotion, framing, limits to rationality means behavioural finance.
Remove options with always, never, or entirely.
Pick the remaining option that matches the school of thought.

Common mistakes in Introduction to Behavioural Finance

Saying behavioural finance claims all investors are irrational all the time.
The name sounds like the opposite of rational, so students overstate it.
Fix: Remember it says investors are normal and subject to systematic biases, not always irrational.
Treating behavioural finance as a branch of accounting or pure statistics.
Students focus on the word finance and forget the psychology link.
Fix: Link it with psychology and decision making. It explains how people decide, not how books are kept.
Assuming traditional finance says every investor is rational at every moment.
The textbook assumption is simplified and then overstated.
Fix: Traditional finance assumes rational behaviour on average, and that irrational traders get cancelled out or corrected by arbitrage.
Mixing up cognitive errors and emotional biases.
Both are called biases and the examples look similar.
Fix: Cognitive errors come from faulty reasoning or information handling. Emotional biases come from feelings and impulse.
Believing behavioural finance makes investing advice unnecessary or markets useless.
Students read criticism of rationality as rejection of all theory.
Fix: It complements traditional finance and helps advisers understand clients and tailor advice.

Worked examples

Example 1

Which of the following best describes the main difference between traditional finance and behavioural finance? (A) Traditional finance assumes investors are rational, while behavioural finance recognises the role of psychology in decisions (B) Traditional finance studies emotions, while behavioural finance studies only tax rules (C) Traditional finance applies only to equity, while behavioural finance applies only to debt (D) Traditional finance assumes markets are always inefficient, while behavioural finance assumes they are always efficient

Show the solution

The question asks about the core difference, so look at the assumption about investors.
Traditional finance assumes rational investors and efficient markets.
Behavioural finance brings in psychology and bounded rationality.
Option B reverses the roles and adds tax, which is irrelevant.
Option C is about asset classes, which is not the distinction.
Option D reverses the market efficiency assumption.

Answer: (A)

Example 2

An investor keeps buying shares of a sector simply because everyone around him is buying it and prices have been rising, ignoring valuation. Which view best explains this behaviour?

Show the solution

The investor is influenced by what others do and by recent price rises, not by analysis of value.
A rational, fully informed investor in traditional finance would assess value and not follow the crowd.
Behaviour driven by crowd influence and psychology is explained by behavioural finance.
Such patterns, when widespread, can contribute to bubbles in market prices.

Answer: Behavioural finance explains it: the investor's decision is driven by psychological influence, not by rational valuation.

Exam tips

Expect direct questions on definitions and the contrast between rational and normal investors. Learn the two sets of assumptions word for word.
Watch for absolute words such as always and never. They usually mark the wrong option.
Scenario questions often describe behaviour without naming it. Identify the school of thought first, then the bias.
Wrong answers are penalised by 25% of the marks for the question, and 2-mark caselet questions cost more. Eliminate options before guessing.

Practice questions from Basics of Behavioural Finance

Introduction to Behavioural Finance: frequently asked questions

What is behavioural finance in simple words?

It is the study of how psychology, emotions and mental shortcuts affect the money decisions of investors and the behaviour of markets. It explains why people often do not act as perfectly rational decision makers.

How is behavioural finance different from traditional finance?

Traditional finance assumes investors are rational and markets are efficient. Behavioural finance accepts that investors are normal people with biases and emotions, and that these can affect decisions and prices.

Why did behavioural finance emerge?

It emerged because observed investor behaviour and market events, such as bubbles and crashes, were hard to explain with the assumption of full rationality. Insights from psychology helped explain these patterns.

Why does behavioural finance matter for an investment adviser?

Knowing a client's likely biases helps the adviser give realistic advice, manage expectations and avoid unsuitable recommendations. It also helps the adviser keep the client invested through market swings.