One way to identify and analyze tone is to look at the writer’s word choice, which we refer to as diction. Emily Dickinson’s poem “Success is Counted Sweetest” is, like most of her poems, very brief--a mere 53 words. Dickinson’s skill as a poet lies in her ability to say a lot in the space of those few words. Let’s look at her diction and see what kind of tone we can identify.
Ne’er (the truncated form of “never”--Dickinson wanted to shave off half a syllable here), sorest need, not one, defeated, dying, forbidden, distant, agonized.
Here are ten words, almost 20 percent of the poem, that communicate the idea of loss and of being denied the joy of victory. When determining a tone it is important to remember that you’re looking for a word that that expresses the artist’s attitude toward his/her work. There is rarely, if ever, just one correct tone to a work, because there is always variation in the readers’ perception of the work.
I would say that the tone of “Success is Counted Sweetest” is mournful. It laments the “agony” (to use one of Dickinson’s own words from the poem) of those who suffer in defeat not just once, but always. But you, and countless other readers, might perceive a different tone, although all would have something to do with how it feels to "ne'er succeed."