Dumbbells add an external load on the body that is immutable. As muscles tire and the load doesn't ease they degrade. The damage they sustain triggers the body's adaptive response and muscle protein synthesis kicks in to repair muscle tissue that has sustained damage due to exercise-induced stress and help it become stronger and larger. Super Strength is a strength-building workout designed specifically to help you achieve your strength goals.
Extra Credit: Do the first set for each exercise to failure.