Choice
"I couldn't do it, I just couldn't do it."
With Glinda crying into his shoulder, berating herself for not going with Elphaba, Fiyero could hardly judge her for her choice. Though he liked to think he would have had the courage to do what Glinda couldn't, he couldn't honestly say he wouldn't have done differently. It was a lot to ask from someone, let alone a teenager, to give up all safeties and guarantees you've ever known.
The question plagued him for years, would he go?
In the end he didn't need to decide – his heart did it for him.