Gallup

Gallup is a company, not a writer. Now, Discover Your Strengths was written by Marcus Buckingham and Donald O. Clifton and published under the firm's name, and the claim is that people improve faster by developing what they are already good at than by repairing what they are not. The book comes with an access code to the assessment, sold now as CliftonStrengths, which is what the whole thing exists to sell. The instrument has reasonable test-retest reliability and much thinner evidence that acting on the results changes performance.