Expectancy

Expectancy is what an average trade earns, worked out as win rate × average win − loss rate × average loss. Above zero, a strategy has an edge. A strategy that wins 35% of the time, makes 3R on a win and loses 1R on a loss earns +0.40R a trade.

Win rate alone says little. A 70% win rate loses money if losses are three times the size of wins. Expectancy combines the two numbers that matter, and over many trades it is what the account grows by, before luck.