A z-score is a distance in standard deviations… a unit of surprise. “z = +2” means “two σ above typical,” not “smart” or “good.” Use z to compare across scales (minutes, points, dollars) and to speak percentile without the drama. The trick isn’t memorizing every table entry; it’s knowing where the tails start to matter for your decision. Decide your “interesting” zone (say |z| ≥ 2), then act on it consistently.
