The insight that the poem gives regarding the sense of self identity is one in which the individual understands more of self when they are apart from others. The poem does not offer a collective notion of self. Rather, the search for "something" regarding truth and understanding is an individualistic notion, one in which individual reflection and understanding happens away from others and from a collective identity.
The opening line of the poem indicates this. The speaker opens the poem with the idea that "Others taunt me" and how the speaker is perceived to assuming a position that is "always wrong to the light." The sense of self offered in these notions is one in which an individual search for truth is not a collective endeavor. It is individualistic. It is away from others. The outside world "taunts" the speaker and criticizes the speaker for pursuing a path that is "wrong." This helps to enhance the sense of self which can only be conceived away from the social notion of the good.
The discovery of truth is a fleeting instant in the poem. The idea of a kernel of truth being present in the eyes of the speaker, only to see it "lost" is reflective of how truth is both fleeting and something that the individual can experience in their grasp only to see it gone. The struggle with which the speaker seeks to better understand this notion of truth is not something to be shared in the presence of others. This would divert from the focus and attention that the speaker needs in order to understand what "truth" actually is. It is an individualistic sense of self that enables the speaker to understand that truth was present "for once, then, something" causes it to dissipate. This sense of self is individualistic and not applicable to a collective notion of the good.