In 1954, a psychologist named Paul Meehl published a small, uncomfortable book. He compared the accuracy of clinical psychologists predicting patient outcomes versus simple statistical formulas built from the same information. The formulas won, in nearly every study he could find.
The finding kept growing. In 2000, William Grove and colleagues pooled 136 studies across medicine, psychology, hiring and parole decisions. The formula did as well as the expert or better in about nine studies out of ten. The experts clearly won in only 8 of the 136. It is one of the most replicated findings in social science, and it applies directly to investing.
I learned this the expensive way. I traded on judgment early in my career and I thought I was good at it. A lot of it was a bull market. That is the whole case for rules, and the rest of this page is the evidence.
01Infographic
Rules vs gut, what the Indian data says
SEBI study of individual F&O traders, FY26 (August 2026); active fund scorecard to 30 June 2026.
- 01Key figures
- 02The flow
- 03The table
| SEBI study year | Individual F&O traders with net losses |
|---|---|
| FY24 | 91.1% |
| FY25 | 90.9% |
| FY26 | 87.7% |
MythWith enough screen time, a good trader learns to feel the market.
FactSEBI found that among F&O traders who lost two years in a row and kept trading, about nine in ten lost again in the third. Experience without a rule mostly repeats the mistake.
Systematic vs discretionary investing
Systematic investing means making investment decisions through a defined, repeatable process, rules applied consistently, without exception, regardless of market conditions or how you're feeling that morning.
Discretionary investing means making decisions based on judgment, intuition, and interpretation. This is how most individual investors and most active fund managers operate.
Decides in the moment
- "I think this auto stock will do well this quarter"
- "Markets feel overvalued right now"
- "I'll hold this, it will come back"
- Changes with mood, news and recent performance
Decides once, in advance
- "Buy the top 30 momentum stocks in the Nifty 500"
- "Rebalance on the first trading day of each month"
- "Sell anything that falls out of the top 30 rank"
- Same process in bull markets and bear markets
The biases that make human judgment unreliable
Our brains evolved as pattern-recognition machines for an environment nothing like financial markets. The field of behavioural finance, pioneered by Daniel Kahneman and Amos Tversky, has catalogued how investors reliably make the same predictable errors.
Kahneman & Tversky, Prospect Theory (NBER)These biases aren't signs of stupidity, they're deeply wired cognitive shortcuts that evolved for an entirely different environment. The problem: financial markets specifically reward people who override these instincts and punish those who follow them.
The evidence from Indian markets
Share of active large cap funds in India that trailed the benchmark, to 30 Jun 2026
- Six months85%
- 3 years80%
- 5 years85%
- 10 years74%
Source: active versus index scorecard for India, mid year 2026. Counts include funds closed or merged during the period.
Two different groups, one lesson. The traders lost mostly to their own reactions and to costs. The fund managers lost mostly to fees and to the difficulty of out guessing a market full of other professionals. A rule does not make you smarter than either. It stops you making the same expensive mistake twice.
Why rules work: four reasons
The honest disclaimer: Systematic strategies are not magic. They have drawdown periods, sometimes long and painful ones. Momentum strategies can fall hard: the Nifty200 Momentum 30 index dropped 30.7% from peak to trough in the two years to 9 October 2026, and was still 21.5% below its starting level. What systematic investing offers is not certainty of good outcomes, it offers a process with known characteristics that removes the emotional errors that cost most investors dearly.
A worked example: April 2025
You do not need to go back to 2020 for a test. On 9 April 2025, after a sharp global sell off, the Nifty 50 closed at 22,399. It had fallen about 5% in three months and the news flow was ugly. Plenty of people sold that week. Three months later, on 9 July 2025, the index stood at 25,476, up 13.7%.
Now take two investors with ₹10 lakh each in a Nifty 50 index fund on 9 January 2025.
| Investor | What they did | Value on 9 Jul 2025 |
|---|---|---|
| Rule follower | Held, as the plan said | About ₹10.83 lakh |
| Gut feel | Sold on 9 Apr 2025, waited for "clarity", stayed out | About ₹9.52 lakh, before tax and costs |
Source: NSE Nifty 50 closes: 23,526.50 (9 Jan 2025), 22,399.15 (9 Apr 2025), 25,476.10 (9 Jul 2025). Price only, before costs and tax. An illustration of the arithmetic, not advice on timing.
The gap is ₹1.3 lakh on ₹10 lakh, in six months, from one decision made on a bad week. And this is the kind version of the story, because the gut investor at least knew when they were wrong. Most do not get back in until the index is higher still.
What would you do?
It is 9 April 2025. Your Nifty 50 index fund is down about 5% since January and the news is ugly.
- Sell and wait for clarity
You sell at 22,399. Three months later, on 9 July 2025, the index is at 25,476, 13.7% higher, and you are watching from cash.
- Stick to the plan
You hold. On 9 July 2025 your fund is about 8.3% above its January level.
- Sell half, keep half
Half your money misses a 13.7% rebound. A rule you half follow is still a gut call.
Nifty 50 closes from NSE, 9 Jan, 9 Apr and 9 Jul 2025, price only. A past episode, not a forecast.
Common mistakes with rules
Overriding the rule "just this once". One exception becomes a habit. If you override, write down why, and check later whether you were right.
Writing a rule you cannot follow. A rule that needs you to trade at 9:15 every morning will be broken on the first busy day. Pick a cadence you can keep.
Judging a rule on three months. Every rule has bad stretches. Judge it on the period it was designed for, against the drawdowns it was expected to have.
Changing the rule after a loss. That is gut feel wearing a lab coat. Change rules only with evidence, and test the change first.
How this shows up in RupeeCase
Every RupeeCase strategy is a written rule: a universe, a ranking, a number of stocks, a weighting and a rebalance cadence, published on the strategy page before you invest. The Allcap Multi Asset strategy, the one this path builds towards, holds 50 momentum ranked stocks from the Nifty Total Market with a 10% debt and 10% gold sleeve, rebalanced every two weeks. On rebalance day you see the order list and approve it; the rule decides, you stay in control of your account.
If rules are better, why do most active funds still use judgment?
Partly habit and partly business. Judgment is easier to sell as a story. Many funds also use rules inside their process, for screening or risk limits, while presenting the final call as judgment.
Does a rule mean I never think?
No. You think hard once, when you choose and test the rule, and again at each scheduled review. You stop thinking at the moments when thinking is least reliable, in the middle of a crash or a rally.
Can a rule fail?
Yes. A rule can stop working if the edge behind it disappears, or simply have a long bad run. That is why the review step exists, and why you size any one rule so that its worst stretch does not force you out.