This is successful because it incorporates both simplicity and a unique design to create an effective logo. The bold words arranged vertically/horizontally as well as the the running shoes allow this t-shirt to stand out. The elements of texture and color are used on the bold letters to create contrast and a sporty effect. Additionally, the design incorporates the principle of unity, and looks professional. 
http://99designs.com/designs/ing-run-something-better-program-needs-t-shirt-t-shirt-design-99designs_10751408_largecrop