We talk about ambition all the time – it's that thing that all business leaders seem to have in abundance, and the thing that your guidance counselor told you that you must possess if you want to get into Yale. In "I, Too, Sing America," the speaker has to have ambition for an even more pressing reason – his survival, his sense of self, and his sense of racial equality. He also possesses a persistent optimism, which manifests itself in the speaker's assurance that one day, he, too, will "be at the table."
By constantly overcoming obstacles throughout the poem, the speaker becomes, in a sense, classically "American."
The main optimistic force in this poem is the speaker's belief in the power of his body.