Alexis did everything right, for a while. He read the books, opened an account, set up a monthly transfer into a boring diversified fund. Then came a bad spring: his portfolio fell 30% in six weeks, every headline promised worse, and one night, unable to sleep, he sold everything to protect what was left. The relief was physical.
The market recovered, as it eventually had every time before, which is the only reason there is a long-run average to talk about. Alexis bought back in a year and a half later, once it felt safe again, at prices higher than the ones he had sold at. Read the sequence slowly: he bought, watched a fall, sold low, watched a rise, bought high. No scammer touched him. No crash took his money; the crash reversed itself. Every euro of his loss was handed over voluntarily, by him, while he felt prudent the entire time.
The psychology of money made the case, following Morgan Housel, that doing well with money has less to do with what you know and more to do with how you behave. That article was about understanding. This one is about defence, because the biggest threat to your money is not a market crash and it is not a fraudster. It is the person holding the phone.
Meet the saboteurs
These are not character flaws. They are standard-issue human wiring, present in everyone, documented for decades. That is the good news: an enemy this predictable can be planned for.
Loss aversion. Daniel Kahneman and Amos Tversky showed that losses hurt roughly twice as much as equivalent gains feel good: losing €100 stings about as hard as winning €200 pleases. In a portfolio this becomes a specific, well-documented mistake. People cling to their losers, because selling would make the loss real and the pain official, and they rush to sell their winners, because banking a gain feels safe. The result is a portfolio that keeps its weeds and pulls its flowers.
Recency bias. Whatever happened in the last six months feels like the new forever. Two good years and your brain quietly concludes that markets simply go up now; two bad months and it concludes the decline is permanent. Both conclusions arrive with total confidence and no evidence beyond "look around." Recency bias is why money floods into funds after they have risen and drains out after they have fallen, which is precisely backwards.
Herd-following. Safety in numbers is ancient and excellent survival advice, and in markets it is how everyone buys the top together. If everyone you know is buying something, prices already contain their enthusiasm; you are not early, you are the crowd. The herd feels safest to join at the exact moment it is most expensive to join.
Overconfidence. Most drivers rate themselves above average, which cannot all be true, and most traders quietly do the same. A few early wins, often pure luck, get filed as skill. Skill justifies bigger positions and more frequent trading, and frequent trading is where returns go to die: in fees, taxes, and mistimed decisions.
FOMO. The fear of missing out, the sense that everyone else is getting rich without you, is the single most expensive emotion in markets. It overrides every question a calm person would ask: what is this, what is it worth, why is it going up. FOMO does not care. FOMO only knows that your colleague doubled his money and you did not, and it will pay any price to make that feeling stop.
The cycle that makes everyone buy high
Put those biases in a crowd and you get the emotional cycle of a market, one of the most repeated patterns in finance. On the way up: optimism, then excitement, then euphoria. Euphoria is the dangerous one, because at the top it does not feel like recklessness. It feels like certainty. Prices have risen for so long that rising looks like a law of nature, the herd is all in, and recency bias supplies the forecast.
Then the turn. Denial first ("a healthy dip"), then fear, then capitulation: the point where holding on hurts more than giving up, and people sell simply to make the feeling stop. At the bottom, despair does not feel like panic. It feels like prudence, like finally being responsible. Which is why the bottom is where the most selling happens.
The damage is measurable. Morningstar's "Mind the Gap" studies compare the returns funds earn with the returns their investors actually receive, and they consistently find a gap: investors earn less than the very funds they own, because of the timing of their own buying and selling. Same fund, worse result, and the entire difference is behaviour.
What one panic costs
Here is the cycle as arithmetic, using Alexis. Assume he holds €10,000 in a broad fund and the market falls 30%. His stake is now worth €7,000. He sells, and waits for it to feel safe, which for most people means the market has climbed back to where it was, a rise of about 43% from the bottom (€7,000 times 1.4286 is €10,000). Then he buys back in.
| Alexis, who sold the bottom | His neighbour, who did nothing | |
|---|---|---|
| Before the fall | €10,000 | €10,000 |
| At the bottom | €7,000 (sells) | €7,000 (holds) |
| After full recovery | €7,000 (buys back) | €10,000 |
The market round-tripped to exactly where it started and took nothing from anyone, yet Alexis is down 30% for good. His neighbour, who spent the crash walking the dog, kept everything. That permanent gap was manufactured entirely by two decisions, both of which felt sensible on the day. (Assumes a clean fall and full recovery for the arithmetic; real paths are messier, but the mechanism, selling low and rebuying high, is exactly what the behaviour-gap studies keep finding.)
You cannot out-discipline your own brain in the moment. The only defence that works is to make the decisions before the moment arrives, and to automate them so the moment never gets a vote.
Remove the fuel: money you do not need
Every bias on the list runs on the same fuel: urgency. Fear needs a deadline, FOMO needs a closing window, panic needs "before it is too late." Remove the need and you remove the urgency, and most of the biases stall on the launch pad.
This is why Stock picking: the honest version insisted on one rule before anything else: only invest money you will not need for years. If next year's rent is in the market, a 30% fall is a genuine emergency and selling may be forced on you at the worst possible price. If the money is truly surplus for a decade, the same fall is a price change on something you were not planning to sell anyway. Alexis's mistake started long before the bad spring: he had invested money he could not emotionally afford to watch fall.
Guardrails: decide once, when you are calm
The useful core of this article is three guardrails. None of them requires willpower on the bad day. That is the whole point of a guardrail.
Automate the contributions. The transfer that leaves the day after payday, same amount into the same fund, is a decision made once by the calm version of you and then executed by a machine with no feelings about headlines. Conscious spending built this plumbing for saving; the same plumbing is the strongest bias defence in investing, because a standing order does not read the news.
Write your rules down in advance. An investment policy sounds like a document for pension funds. Yours needs three sentences: what I buy, when I add, what would make me sell. For example: "I buy one broad, diversified fund. I add €200 the day after every payday. I sell only when the goal this money is for arrives, never because prices moved." Write it while you are calm and keep it where you will find it. When the market is on fire, your only job is to obey the calmest version of yourself, who thoughtfully left instructions.
Stop checking the portfolio daily. Over a single day, a broad market is close to a coin flip that is tilted slightly upward; over decades, the upward tilt is most of the story. Check daily and roughly half of what you see is a loss, and loss aversion bills you double for every one of them: torture, on a subscription. Check yearly and you mostly see the trend. It is the same portfolio either way, but the daily habit quietly erodes exactly the discipline the other two guardrails were built to protect.
Do this now
Write your three-sentence investment policy this week: what I buy, when I add, what would make me sell. If you do not invest yet, write it anyway; it costs ten minutes and it will be waiting when you start. Then take the portfolio app off your phone's home screen and switch off its notifications. You are not hiding from your money. You are choosing which version of you gets to make the decisions.
Next in the series: Get-rich-quick traps and scams, because the biases you just met are exactly the buttons a scammer is trained to press.