Summary of 10 Investment Biases and How to Avoid Their Traps /By Longtunman
"Missing the bus," "Selling too soon," or "Being stuck at the top."
These are symptoms that every investor in stocks, funds, or various financial assets has likely encountered.
One of the primary causes of these situations is "Investor Bias"—the emotional influence that constantly affects investors trying to build their portfolios.
Longtunman will introduce you to 10 types of investment biases that occur in long-term investing. Use this as a checklist to see which biases are currently in your mind, along with solutions to refine your mindset so you don't fall victim to yourself again.
1. Confirmation Bias – The "Favorite Stock" Bias
This occurs when an investor likes or dislikes a particular stock too much. For example:
If we are head-over-heels for "Stock A," we will try to pick out or accept only positive information to support our belief as to why we like it and want to buy it.
Conversely, if we have a bias against "Stock B," we will seek out only negative information to support our dislike, leading us to avoid buying it altogether.
- The Trap: This bias prevents us from looking at an investment holistically. We only see the opportunities in Stock A and only see the risks in Stock B.
- The Solution: Try looking at the stock from the opposite perspective. If you see an opportunity in Stock A, ask yourself: "What are the risks?" or "What reasons would make me not want to buy this?"
You might also exchange ideas with neutral friends or peers. Ask those who dislike Stock A why they feel that way to help weigh your decision more objectively.
2. Herd Behavior – The "Follow the Crowd" Bias
This happens when investors make buy or sell decisions based on what the majority is doing, rather than doing their own homework or analysis.
- The Trap: When most people are buying, we follow suit due to "FOMO" (Fear Of Missing Out). This often leads to buying stocks at inflated prices that we don't truly understand. On the flip side, when the crowd panics and sells, we may follow them, sometimes selling at prices far below the intrinsic value.
- The Solution: Practice thinking, analyzing, and valuing businesses on your own to ensure independent decision-making.
3. Authority Bias – Trusting the "Gurus" Too Much
This occurs when investors tend to over-rely on "experts," "gurus," or analysts from various institutions because of their superior experience and knowledge.
We often forget that these experts can make mistakes just like anyone else.
- The Trap: This leads to a lack of independent analysis. Excessive reliance on authorities can make us vulnerable to rumors or price manipulation.
- The Solution: Practice valuing businesses yourself. You can use a guru's pick as a starting point for your own homework, but always remind yourself that even the "gods" of investing can fail.
4. Anchoring Bias – Stuck on the First Piece of Information
This involves using the first number or piece of information as a "mental anchor" for decision-making. For example:
Stock A once hit 100 Baht. Now it has dropped to 70 Baht. Even if the valuation is still high, an investor might buy it at 70 Baht simply because it looks "cheap" compared to the old price of 100 Baht.
- The Trap: It makes investors believe a stock is cheap based on historical data. In reality, past prices have no influence on future performance. A falling price might be due to deteriorating fundamentals or lost market share. Sometimes, the past price was simply an overvaluation.
- The Solution: Let go of past prices. Focus on the current situation and the company's future potential. Ask why the price dropped and check if it’s a short-term factor or a shift in long-term growth.
5. Loss Aversion – The Fear of Realizing a Loss
This bias stems from being more sensitive to the pain of loss than the joy of gain. For example, if you sell two stocks—one with a 10,000 Baht profit and one with a 10,000 Baht loss—you will feel the pain of the loss much more intensely than the happiness from the profit.
- The Trap: This leads to "selling your winners" (good stocks) to lock in gains while "holding your losers" (bad stocks) in the hope that they will bounce back, even if their fundamentals have fundamentally changed.
- The Solution: Forget your initial cost. Evaluate the business's current value to decide whether to buy more, hold, or "Cut Loss." Consider the "opportunity cost"—the money stuck in a losing stock could be working harder in a stock with better growth prospects.
6. Overconfidence Bias – Excessive Self-Belief
This occurs when an investor overestimates their own ability to pick stocks or becomes overly certain about a specific company's success. You might believe "this stock will grow exactly this much" or "competitors can't touch this business."
- The Trap: It leads to over-concentration in a single stock, causing the investor to ignore hidden risks.
- The Solution: Consistently diversify your risks. Do not concentrate your entire portfolio into just a few stocks you are "certain" about. If you are wrong, diversification ensures you aren't devastated.
7. Disposition Effect – Emotional Trading
This is the tendency to sell profitable stocks too quickly while refusing to sell losing stocks for a long time.
- The Trap: This leads to inefficient capital management. You might "sell the pig" (sell a great stock too early) on a company with long-term potential, or "stay on the mountain" (hold a losing stock) on a company losing its competitive edge.
- The Solution: Keep a journal. Write down why you bought a stock in the first place and why you want to sell it today. Review these reasons to see if your decisions are driven by logic or emotion.
8. Framing Effect – Influence of Presentation
This occurs when the same information from the same company is presented in different ways, affecting an investor's decision. For example:
Option A: A CEO announces 20% revenue growth and a 40% increase in store branches.
Option B: A CEO announces 20% revenue growth but notes that "Same-Store Sales" decreased by 14.3%.
Even if the financial results are identical, Option A sounds much better than Option B.
- The Trap: If you aren't careful, you might be swayed by the "growth story" of new branches (Option A) while ignoring the declining health of existing stores.
- The Solution: Avoid listening to management or media through a single lens. Read official documents like quarterly financial statements or Annual Reports in detail. Compare the data with competitors in the same industry to see who truly has the better performance.
9. Recency Bias – Overweighting Recent Data
This happens when investors give too much weight to recent news or performance. For example, buying a fund because it was the "top performer" last year, believing it will automatically repeat that success. Or selling a stock during a sharp dip based solely on short-term negative news.
- The Trap: Investors make impulsive decisions based on recent "stories" without considering if the price is below intrinsic value or if recent drivers will persist in the future.
- The Solution: Look back at the fundamentals. Check if recent news actually changes the long-term prospects. Always remember that past/current returns do not guarantee future results.
10. Cognitive Dissonance – Deep-Rooted Beliefs
This occurs when an investor is so deeply committed to a stock that they reject bad news, ignore new facts, or deny changing situations.
- The Trap: You become "in love" with the company. When bad news hits—such as management fraud or accounting irregularities—you might distort the truth, calling it a "rumor" or hoping a new leader will magically fix everything, even when the signs say otherwise.
- The Solution: Accept that in the world of investing, you won't always be right. As George Soros said:
“It's not whether you're right or wrong that's important, but how much money you make when you're right and how much you lose when you're wrong.”
This mindset emphasizes that risk diversification is a key tool to protect yourself from the dangers of Cognitive Dissonance.
These are the 10 forms of bias that occur while building a long-term portfolio. These biases can strike whenever there is news, financial reports, or market shifts. The best way to handle them is to have a system in place to refine our mindset and minimize these biases as much as possible.