The direction you cut chicken breasts matters significantly due to the muscle fibers. In a whole chicken breast, the muscle fibers run in different directions, and you can spot where by simply taking a closer look or running your fingers over it. Cutting against the grain gives you shorter muscle fibers in each piece, resulting in tender bites when cooked. The muscle fibers are longer when cut with the grain; therefore, pieces won't be as tender. For this reason alone, it's best to cut chicken against the grain.