The piece of textual evidence that best supports the theme that the journey of life leads us to discover who we are is:
> “My eyes strayed far and wide before I shut them and said `Here art thou!'”
This line suggests that the speaker has been on a journey of discovery, and that they have finally come to a place of self-awareness. They have looked far and wide, and they have finally found themselves. This is a powerful statement about the journey of life, and it suggests that the journey is ultimately about discovering who we are.
The other options are not as strong as this one. The first option is about the complexity of training, which is not directly related to the theme of self-discovery. The second option is about the length of a journey, which is also not directly related to the theme of self-discovery. The third option is about the speaker finding something, but it is not clear what they are finding or why it is significant.
Overall, the line “My eyes strayed far and wide before I shut them and said `Here art thou!'” is the strongest piece of textual evidence that supports the theme that the journey of life leads us to discover who we are.