Exploring Indecision and Identity

In the following excerpt from a contemporary novel, the protagonist reflects on their past experiences during a pivotal moment of crisis:

"As I look back on the years, the fleeting moments that seemed trivial then now stand as towering reminders of choices unmade. Each whisper of nostalgia is laced with the sharp pang of 'what if,' turning my heart into a battlefield. It was never the obvious decisions that haunted me; rather, it was the silence surrounding my indecision that forged my identity, shaping who I have become. There lies a world of possibility in the paths I could have taken, yet here I stand, shackled by the weight of my own hesitation, as the specters of opportunity loom over me.”

Based on this passage, what is the main theme concerning the protagonist's reflections?