The Agile Manifesto puts the value of "individuals and interactions over processes and tools". Meaning that a conversation is where the work starts. Meaning that if your processes/tools are getting in the way of human interaction then you aren't practicing this value and not getting the benefits of Agile. For example, work requests delivered long-form via email is not an interactive process.
Agile processes generally use User Stories as a starting point for any development work. Just what is a User Story? It's really a placeholder for a conversation, no details except a concise introduction of the user's goal - "As an end-user, I want to print my essay so that I can mark it up with red-ink and make revisions based on the markup." This is the user's perspective. It isn't even about the user story, it's really just there to keep track of something.
As a technologist, I might want to poo-poo the idea of printing and using ink...or even wasting paper as an environmentalist...but this user story is her story, not mine. Through conversation, there may be a change of heart, but that comes into the fold of negotiations.
Through the initial conversation, we should come up with some Acceptance Criteria. It's documented, but not written in stone - it's just a first pass. It should be fairly basic and relatively quick to implement. May not be complete yet, but could be. The Acceptance Criteria is also known as the Acceptance Test...User Test...Story Test. It should describe how the user would validate the implementation (then we automate it, but that's for another time).
"When I click a print button, the essay should print. I should be able to go to my printer and get the printed essay from the printer. All pages should be there."
What can go wrong there? If have any experience with printers, we know there are too many ways that can fail! Printer out of ink, paper, jammed, just not having it that day, not connected, off. Computer/OS not happy with printer config, dialog comes up before printing, not connected to network. Network failure. Mercury in retrograde.
Perhaps in some future world, printing will just work, but for now we need to revise the Acceptance Test...that's why we need to work on it together...
"I can't promise the essay will print, but I can make it so that there's a print button which will tell your computer to print all pages of the essay to the default printer, or I can have it launch the print dialog."
There's some negotiation. There's supposed to be, it's another Value. But first, we should try the simplest thing that works...do whatever the OS does when you want to print. And that just might get the job done.
Without the conversation, we'd have wasted half the project schedule on documenting something that was nearly impossible and then attempting to implement something that was doomed to fail anyways...at least when Mercury isn't playing nice!