Consider a trader running a 70% win rate. Sounds impressive. But each win returns 0.5R and each loss costs 2R. Over 10 trades: 7 wins at 0.5R = +3.5R, 3 losses at 2R = -6R. Net result: -2.5R. A profitable-looking win rate quietly bankrupts the account. This is not a theoretical edge case — it happens constantly.

The Turtle Traders, trained by Richard Dennis in the 1980s, operated with win rates often below 40%. Some estimates put it closer to 35%. They were profitable not because they won often, but because their average winner dwarfed their average loser. Position sizing and fixed-percentage risk rules did the structural work that "gut feel" never can.

CONCEPTA 35% win rate with a 3:1 reward-to-risk ratio outperforms a 70% win rate with a 0.5:1 ratio — every time, over every sample size.
WARNINGSizing positions by "feel" rather than fixed percentage risk is how accounts with high win rates still go to zero.
KEY IDEAExpectancy = (Win Rate × Avg Win) − (Loss Rate × Avg Loss). Win rate is only one variable in that equation.

The Turtles used 1% to 2% of account equity per trade, adjusted by volatility using Average True Range (ATR). If volatility doubled, position size halved. The rule was mechanical, not optional. A 10-trade losing streak at 1% risk per trade produces a 9.6% drawdown — painful but survivable. At 10% risk per trade, that same streak is an 65% drawdown. Recovery from 65% requires a 186% gain just to break even.

Drawdown After 10 Consecutive Losses1% risk = 9.6% drawdown5% risk = 40.1% drawdown10% risk = 65.1% drawdown0%Drawdown %65%+1%5%10%

Implementing a rules-based approach means calculating position size before every trade, not after. The formula is straightforward: Position Size = (Account Equity × Risk %) ÷ (Entry Price − Stop Loss). No exceptions for "high conviction" setups — conviction is not a risk management tool. Traders wanting to go deeper on expectancy and position sizing will find structured explanations at Investopedia's risk management reference, while the original Turtle Trading rules are well documented on Wikipedia's Turtle trading page. The mathematical foundation of expectancy is covered thoroughly at Investopedia's expected value explainer.

Win rate is a vanity metric. Expectancy, drawdown control, and position sizing are the load-bearing walls of any trading system.

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