Yet, Perry delivered strong self-empowering anthems, such as "Roar," "Power" and "Firework," which were inspiring, soaring tunes. But no one can be all things all of the time. Perry's determined mutability has taken her far, from her solid pop songwriting ("Teenage Dream") to the darkly seductive, EDM-infused "Dark Horse," Perry has been a barometer for radio hits as well as a champion for important social causes. But at the United Center, tenacity wasn't enough to keep her fully in step with the times.