Interactive Tool
The investor in the mirror
The other tools show that timing the market doesn't work. This one shows why we keep trying — and what it costs. The biggest threat to your returns usually isn't a crash; it's how you react to one. Meet the behavior gap and the wiring behind it — then step into the Bias Arcade and let eight short experiments, adapted from the classic studies, measure that wiring in you.
Two investors put $10,000 in the whole US market in 1990. One never touches it. The other panics in downturns. Set how the panicker behaves:
Method: real daily US total returns, 1990–2026 (Fama–French). Cash earns nothing while out (a simplification). The point isn't the exact figure — it's the direction, which barely ever reverses. Educational only, not advice.
Staying put vs. selling the dips
The shaded stretches are when the panicker sat in cash, having sold near the bottom and waited to buy back. The market's best days cluster right next to its worst, so sitting out the rebound is what does the damage.
- Buy & hold ends at
- $457,006
- Panic-seller ends at
- $151,044
- Times they panicked
- 11
- Years out of the market
- 7.9
This is the behavior gap: the distance between the return investments earn and the lower return investors actually keep, because we buy after things feel good and sell after they feel bad. Studies of real fund flows (Morningstar's "Mind the Gap," and DALBAR before it) find the average investor gives up on the order of a percentage point or more a year to exactly this. The fix is almost insultingly simple and almost impossibly hard: do nothing. Pick an allocation you can hold through a crash, automate it, and stop watching. Educational only, not advice.
The gap between what you earn and what you keep
- Investments earn more than investors do. Fund returns measure a dollar left alone. Investor returns measure the dollars people actually add and pull out — and because we add after good runs and pull out after crashes, the second number is reliably lower. That shortfall is the behavior gap.
- The worst moments feel the most rational. Selling in a crash isn't stupidity; it's loss aversion, recency, and herding all firing at once. The feeling that you must "do something" is exactly the feeling to distrust.
- The cure is a plan, not more willpower. You can't out- discipline your own nervous system in the moment. You can decide your allocation in calm times, automate it, and remove the decision — so a bad week has nothing to act on.
The simulation assumes idle cash earns nothing and ignores taxes, to keep the mechanism clear; the exact number will vary, but the direction almost never does. Educational only, not financial advice.
Sources & further reading
How this tool was made
The behavior-gap simulation runs on real daily US market returns (Fama–French, 1990–present), and the fund-level gaps are computed from CRSP mutual-fund records. In the arcade, “real or random” shows genuine market history against volatility-matched coin flips, and the quiz answers are computed from the historical return data rather than written by hand; the vignettes are adapted from the published experiments cited above.
Research
- Kahneman, D., & Tversky, A. (1979). “Prospect Theory: An Analysis of Decision under Risk.” Econometrica 47(2): 263–291. The foundation of behavioral finance; losses loom larger than equivalent gains.
- Tversky, A., & Kahneman, D. (1992). “Advances in Prospect Theory: Cumulative Representation of Uncertainty.” Journal of Risk and Uncertainty 5(4): 297–323. Cumulative prospect theory, and the source of the widely quoted loss-aversion coefficient of about 2.25.
- Rabin, M. (2000). “Risk Aversion and Expected-Utility Theory: A Calibration Theorem.” Econometrica 68(5): 1281–1292. Turning down small favorable gambles is inconsistent with any plausible expected-utility risk aversion over wealth — the argument that loss aversion, not diminishing marginal utility, explains it.
- Russo, J. E., & Schoemaker, P. J. H. (1989). Decision Traps: Ten Barriers to Brilliant Decision-Making and How to Overcome Them. Doubleday. Managers asked for 90%-confidence ranges trapped the true value only about half the time — the calibration result the arcade's quiz reproduces.
- Barber, B. M., & Odean, T. (2000). “Trading Is Hazardous to Your Wealth: The Common Stock Investment Performance of Individual Investors.” The Journal of Finance 55(2): 773–806. The more households traded, the worse they did: the most active fifth trailed the market by about 6.5 points a year, mostly from trading costs.
- Ptak, J. (2026). “Mind the Gap 2026: US stock fund investors made history; crypto mavens stumbled.” Morningstar Portfolio and Planning Research. The authoritative investor-return-gap study. Over the 10 years to Dec. 2025, the average dollar earned 8.7%/yr vs. funds' 9.9% total return — a ~1.2pp gap; the US-equity gap was the smallest of any category at ~0.4pp, close to this tool's independently computed CRSP medians (~0.3pp for US-equity funds, ~0.5pp across all funds; asset-weighted, our gap is roughly zero). The gap widens with category volatility (sector and alternative funds worst).
- Tversky, A., & Kahneman, D. (1974). “Judgment under Uncertainty: Heuristics and Biases.” Science 185(4157): 1124–1131. Anchoring, availability, and representativeness — including the wheel-of-fortune anchoring experiment the arcade's 'wheel' game recreates.
- Tversky, A., & Kahneman, D. (1981). “The Framing of Decisions and the Psychology of Choice.” Science 211(4481): 453–458. Identical outcomes, opposite choices when worded as gains vs losses — the design behind the arcade's framing game.
- Shefrin, H., & Statman, M. (1985). “The Disposition to Sell Winners Too Early and Ride Losers Too Long: Theory and Evidence.” Journal of Finance 40(3): 777–790. Named the disposition effect the arcade's 'Sell something' game measures.
- Odean, T. (1998). “Are Investors Reluctant to Realize Their Losses?” Journal of Finance 53(5): 1775–1798. 10,000 brokerage accounts: investors realize gains far more readily than losses, and the winners they sell go on to beat the losers they keep.
- Arkes, H. R., & Blumer, C. (1985). “The Psychology of Sunk Cost.” Organizational Behavior and Human Decision Processes 35(1): 124–140. Money already spent keeps voting on decisions it can't affect — the arcade's sunk-cost vignettes.
- Baron, J., & Hershey, J. C. (1988). “Outcome Bias in Decision Evaluation.” Journal of Personality and Social Psychology 54(4): 569–579. Identical decisions judged differently by how the dice landed — the arcade's 'Good call?' game.
- Alpert, M., & Raiffa, H. (1982). “A Progress Report on the Training of Probability Assessors.” in Kahneman, Slovic & Tversky (eds.), Judgment under Uncertainty. The confidence-interval calibration test (first circulated 1969): asked for ranges they were 98% sure of, subjects' ranges missed the truth over 40% of the time. The '90% sure, right about half the time' version is Russo & Schoemaker (1989).
- Asch, S. E. (1955). “Opinions and Social Pressure.” Scientific American 193(5): 31–35. The line-length conformity experiments: 75% of subjects denied their own eyes at least once to agree with a group — the arcade's 'crowd' game.
- Bikhchandani, S., Hirshleifer, D., & Welch, I. (1992). “A Theory of Fads, Fashion, Custom, and Cultural Change as Informational Cascades.” Journal of Political Economy 100(5): 992–1026. How rational copying snowballs into cascades and manias.
- Kahneman, D., Knetsch, J. L., & Thaler, R. H. (1990). “Experimental Tests of the Endowment Effect and the Coase Theorem.” Journal of Political Economy 98(6): 1325–1348. The coffee-mug experiments: owners demand about twice what buyers will pay for the identical item — the arcade's 'Yours to sell' game.
- Fischhoff, B. (1975). “Hindsight ≠ Foresight: The Effect of Outcome Knowledge on Judgment under Uncertainty.” Journal of Experimental Psychology: Human Perception and Performance 1(3): 288–299. Creeping determinism: knowing an outcome inflates how predictable it feels — the arcade's 'You knew it all along' game.
Data
- Kenneth R. French Data Library, Tuck School of Business, Dartmouth College. Data © Eugene F. Fama and Kenneth R. French. The library publishes no formal license; we ship derived series (daily market returns, regional monthly returns, factor summaries) with attribution, not the library's files.
- CRSP Survivor-Bias-Free US Mutual Fund Database, Center for Research in Security Prices, LLC, via WRDS. Source: CRSP®, Center for Research in Security Prices, The University of Chicago. Used with permission. All rights reserved. The behavior gap is computed from fund monthly returns and net assets; only universe-level aggregates and a few anonymized illustrative cases (described by era and category, not named) are published — no per-fund panel is redistributed. Pending written confirmation of the licence's scope for public educational use.
- Historical Returns on Stocks, Bonds, Bills & Real Estate — United States, Aswath Damodaran, NYU Stern School of Business. Annual series from 1928 (histretSP.xls), published by the author without stated usage terms; used with attribution.
Educational use only, not financial advice. Every figure traces back to the sources above or to the inputs you set — the full method and the source code are public.