Read the excerpt from "Thomas Edison: The Master of Improvement.”

It was this same stubborn resolve that made Edison’s lightbulb more successful than Swan’s. Edison thought that the secret to a better bulb could be found in the filament. He simply needed to figure out what type of material worked best. Edison tried metal first. Then he tried different kinds of wood, coconut fiber, and even the hair from a friend’s beard!

Which phrase from the excerpt best supports the author’s view that Edison’s determination helped him succeed?