Expectancy
Expectancy is the average amount a strategy makes or loses per trade over many trades: (win rate × average win) − (loss rate × average loss). A positive number is what "having an edge" means.
With a 40% win rate, a $300 average win, and a $150 average loss: 0.40 × $300 − 0.60 × $150 = $120 − $90 = +$30 per trade. Over 20 trades that projects to about $600 — if the future resembles the sample, which is the standing caveat with every expectancy figure, since edges shift as market conditions do.
Quoting expectancy in R-multiples — average R per trade — makes it independent of account size and comparable across strategies. It also needs a real sample behind it: a few dozen journaled trades or a careful backtest, not five memorable wins.
In a prop-firm challenge
A challenge is a small-sample test of expectancy under constraints. Deadlines and targets tempt traders to raise size even though expectancy is unchanged — which only raises variance against the daily loss limit. A modest positive expectancy executed at survivable size passes more attempts than a strong edge traded too large, which is much of the honest answer to how long passing takes.