The roulette wheel fallacy, also known as the Monte Carlo fallacy, is a logical misconception that can lead investors to make poor decisions based on flawed reasoning about random events. This fallacy stems from the belief that if something hasn't occurred for an extended period, it becomes "due" and more likely to happen in the future. However, this line of thinking fails to account for the fact that each spin of the roulette wheel or each trade in the market is an independent event, unaffected by previous outcomes. The probability remains constant regardless of past results.
Examples for Investors
Buying a Stock After a Series of Losses: Imagine a stock that has declined for several consecutive days or weeks. An investor might think, "This stock has been falling for so long, it's due for a rebound soon." And they decide to buy shares based on that premise. However, each day's stock price movement is an independent event, unrelated to what happened previously. The fact that the stock has fallen doesn't make it any more or less likely to rise the next day. The roulette wheel fallacy makes the investor believe a rebound is imminent when, in reality, the stock could continue declining.
Holding a Losing Position Too Long: Let's say an investor buys shares of a company, and the stock price begins to drop steadily. They think to themselves, "I've already lost so much on this trade; if I hold on, it's bound to recover eventually." This reasoning falls into the roulette wheel trap. Just because the stock has experienced a string of losses doesn't mean a gain is destined to follow. Each day's price movement is independent, and holding onto the losing position based on the misguided notion that it's "due" for a rebound can lead to further losses.
Chasing "Hot" Investments: On the flip side, investors might be tempted to chase investments that have been delivering consistent gains, thinking that the winning streak is likely to continue. "This stock/fund/asset has been performing so well lately; it's due to keep going up." However, as with roulette spins or daily stock movements, each period's investment performance is independent of the last. A series of positive returns does not increase the probability of further gains. Succumbing to the roulette wheel fallacy in this case can lead investors to buy into an investment at an inopportune time, just before a potential downturn.
The Solution: Understanding Probabilities
To avoid falling victim to the roulette wheel fallacy, investors must understand that probabilities in financial markets (and life in general) are not influenced by past occurrences. Each event, each trade, and each price movement is independent and has a fixed probability based on the underlying factors, not on what has happened previously. While past performance can provide valuable insights and help identify trends, it should never be the sole basis for investing decisions. Investors should conduct thorough research, analyze fundamentals, and make rational choices based on probabilities and sound strategies, not on the misguided belief that something is "due" to happen based on recent outcomes.
Gambler's Fallacy in Trading
The gambler's fallacy is a close cousin of the roulette wheel fallacy and can also lead investors astray. This fallacy involves thinking that after a long streak of one outcome, the opposite outcome is now more likely. For example, if a trader keeps losing money on a series of trades, the gambler's fallacy might tempt them to hold onto a losing position. They think "My luck has to turn around soon, so I'll hold on and wait for the rebound." In reality, the probability of winning or losing on the next trade is completely independent of the previous streak.
Mean Reversion Confusion
Some investors may conflate the idea of mean reversion with the roulette wheel fallacy. Mean reversion suggests that over long periods, asset prices and returns will tend to revert toward their long-term averages or means. However, confusing short-term streaks or runs with true long-term mean reversion can open the door to the roulette fallacy way of thinking. Just because an asset has strayed from its average for a while doesn't necessarily mean a reversal is imminent.
Sample Size Insensitivity
The roulette wheel fallacy is exacerbated by human beings' tendency to be insensitive to sample size. A small number of observations (e.g. a stock rising for 3 days) can feel very meaningful, even though the sample is too small to make any statistical inferences. Seasoned investors learn to look at price movements and trading results over long periods involving many observations before drawing any conclusions about probability or likely future events.
The Hot Hand Fallacy
Related to the roulette wheel fallacy is the "hot hand" fallacy - the belief that whatever is happening now is more likely to continue. If a stock has been rising, the hot hand intuition says it's more likely to keep rising. If a trader is on a winning streak, they feel they can't lose. This stems from the same flawed logic as the roulette fallacy - treating statistically independent events as being connected and influencing one another's probabilities.
To counteract fallacious thinking around probabilities, investors should develop rules-based systems and trading strategies that rely on objectivity rather than cognitive biases. Maintaining disciplined position-sizing, using stop-losses, and basing decisions on fundamentals rather than recent runs of success or failure are critical. With education and awareness of the roulette wheel and related fallacies, investors can overcome misleading intuitions and make higher probability decisions in markets driven by randomness.