The Common Core State Standards (CCSSI 2010) for Mathematical Practice have relevance even for those not in CCSS states because they describe the habits of mind that mathematicians--professionals as well as proficient school-age learners--use when doing mathematics. They provide a language to discuss aspects of mathematical practice that are of value in all endeavors that require analytic thinking. Unlike the content standards, which are tightly targeted to specific grades, the practice standards are intended to apply across all content areas and at all grades, acquiring greater depth and broader application over the years. For studying new problems or building new theories, mathematicians often use the practice of trying concrete examples, looking for regularity in the reasoning, and describing the pattern in the reasoning. The CCSS describes this practice as MP 8. To make sense of MP 8, this article illustrates what "repeated reasoning" means, why looking for and expressing regularity in it is such a valuable mathematical habit of mind, and how that differs from analyzing structure (MP 7) and from finding patterns in numerical results.