Foundations · Lesson 17 · Beginner
Thinking in probabilities
You think in series and R units and separate process from outcome.
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The series is what counts
Every single trade is uncertain, but over a large series a positive edge plays out. An edge only needs to be just above 50 percent, combined with strict risk control.
The key metric for this is expectancy, the expected value: your average gain or loss per trade across the whole series. If it is positive, you make money over time, even when individual trades lose.
Process before outcome
A good trade can lose money, a bad one can win. Count a cleanly stopped-out small loss as a good trade, and think in R units instead of USDT.
Switch between 10 and 500 trades and see how the edge only becomes visible over the series.
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Rate three trades by process, not by outcome.
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The key points at a glance
- An edge only plays out over a large series, not on the single trade.
- A good trade can lose, a bad one can win. Judge the process.
Deep dive
Why win rate is overrated: payoff beats win rate
Beginners chase a high win rate, pros chase the ratio. Many of the best traders win only around 40 percent of their trades and are still highly profitable, because their winners are much bigger than their losers.
- Taleb: a 35 percent win rate with 3:1 is profitable.
- A 90 percent win rate with an open loss is a sucker bet.
- Standard recommendation: reward-to-risk of at least 2:1, better 3:1.
- The main benefit of good strategies: closing losers faster.
Calculating expectancy: the one metric that counts
Expectancy is your average profit per trade across the series, combining win rate and payoff into a single number. Example: 40 percent winners at 3R each, 60 percent losers at 1R each gives 0.4 times 3 minus 0.6 times 1, so plus 0.6R per trade.
The mistake is treating a single trade as meaningful. Every trade is as uncertain as a single spin of the roulette wheel, the edge only plays out over the series. That is why you think in R units instead of USDT.
Process over outcome: do not celebrate the lucky gamble
A good trade can lose money, a dumb gamble can win. A trade stopped out cleanly according to plan is good, an entry without a stop that happens to win is bad, because the process was gambling.
The most dangerous moment is the rule break that happened to win: your brain celebrates exactly the behavior that ruins you. Kahneman calls this outcome bias. Keep a journal and mark every rule break as a mistake, whether or not it made money.
Sources: Douglas, Schwager, Kahneman
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