Crossroads
Most crossroads in life tend to pass you by before you realize that you've made a choice.
Glinda thought she'd only crossed one major bridge: choosing to not go with Elphaba (a decision she rarely reconsidered, for fear of what she'd think of herself). None of the other choices she'd made since had been as heart wrenching or difficult, so surely they couldn't have mattered as much?
Yet those other decisions somehow led to her being lifted up as Glinda the Good, opponent of the Wicked Witch. Addressing the citizens of Oz, she wondered exactly how many bridges she'd missed.