If I had to teach this in one paragraph, I would start here: expected value is about weighted outcomes, not about being "right" most of the time. Three quick checks before you act: 1. Name the mechanism in plain English: Investors often obsess over hit rate because it feels psychologically satisfying. Expected value asks a better question: what do wins and losses contribute after probability and payoff size are both counted? 2. Say why it matters for behavior or portfolio decisions: That is the foundation under position sizing, trade filtering and portfolio discipline. 3. Set the review question: If you had to teach this without jargon, what would you tell someone to monitor first? In real life: A setup that wins 40% of the time can still be excellent if the upside meaningfully dominates the downside. Common slip: The most common error is optimizing for comfort instead of expectancy. $$ EV = \sum_i p_i \cdot x_i $$ Plain English: Expected value is the probability-weighted average of all outcomes. That is usually where the edge is: not in the vocabulary, but in the structure underneath it.