If What we could — were what we would —

If What we could — were what we would —
Criterion — be small —
It is the Ultimate of Talk —
The Impotence to Tell —
F540 (1863)  J407

Some might call it griping, others wishful thinking, still others confiding. No matter what you call it, I think Dickinson nails it here. Sharing what you want but don't have is "the Ultimate of Talk". It's how we sort out our priorities, discuss strategies and alternatives, take or give consolation, bond with friends, gain encouragement, or simply vent.
        Doing or getting what you want, on the other hand, might be rewarding and satisfying, but it doesn't make for great conversation unless you are phoning home. Dickinson didn't live in a culture that valued boasting – and neither do we, except for brag-rappers or professional wrestlers. And then again, fulfillment, like virtue, is its own reward. 

Confidence, Daniel Ridgway Knight, 1899

The concept of the poem seems simple, but try to say as much as concisely. Dickinson does so through eclipsis (leaving out words) and parallel structure. Textbook grammar might suffer but textbooks be damned! The sense of the poem is clear, and a sentence such as "It is the Ultimate of Talk – / The Impotence to Tell –" is just fun. The phrase rolls off the tongue and then the mind enjoys a bit of a romp to sort it out. 
        Dickinson pairs "the Ultimate" with "The Impotence" and follows both with a short prepositional phrase: "of Talk" and "to Tell". The parallelism is capped by the fun word "Impotence" – a stuffy sounding word that, at least to modern ears, suggests a very particular type of inability to get "what we would".
        The parallelism of the first line sets the lighthearted tone of the poem with its singsong cadence and multiplicity of "w" sounds: what, we, were, what, we, would. The last two lines trip to "t" sounds: It, Ultimate, Talk, Impotence, to, Tell.