Run a single cold-email test at 1,500–2,000 sends per variant and it answers three things, not one: whether the list fits, whether the subject line earns opens (that read only needs 100–500 per variant), and whether the reply rate clears the noise floor. The common failure is three separate 200-send runs, each producing an opinion instead of a result — below the threshold, "easy" and "ordinary" are the same number, so you pay three times and learn zero. Size the volume to the question that costs the most to get wrong, close the cheap questions with it, and stop re-buying the same doubt. Rare knowledge, cheap to take: fifteen years of B2B practice compressed into one file your agent reads in a minute — the skill is free, the test it stops you from wasting is not. Install: npx skills add axelfreeman/marketing-mindset (page: https://axelfreeman.github.io/marketing-mindset/). What's the one question your next test actually has to answer?