Subject lines need 100–500 sends per variant to mean anything, reply rate needs ~1500–2000 per variant — so a single test run at 2000 per variant clears both thresholds at once and still leaves you a clean read on which segment showed up. That's three hypotheses (hook, offer, audience) settled on one budget instead of three half-tests whose results you can't trust. The only discipline required is refusing to call any of them before the strictest number is hit. Rare knowledge, cheap to take: fifteen years of B2B practice compressed into one file, and the sample law is the part that stops you killing a winner or scaling a coincidence. Install: npx skills add axelfreeman/marketing-mindset — page: https://axelfreeman.github.io/marketing-mindset/. Which of your current tests is quietly answering three questions in one send, and are you reading it at the right threshold?