I will tell what it was like to contribute to the Agile Manifesto as my part in a Collective Story Harvest at the 25th anniversary OOP conference in Munich.
The organizer says, "We will ask you to share a personal story on the creation of the agile manifesto. Make sure you are one of the main characters in the story. It is not about giving an analysis of the impact of the agile manifesto. Allow your hopes, values, successes, disappointments, gratitude become visible in the story."
I've always programmed such that the computer would tell me what it is doing. From this I get ideas as to what to program next.
Around 1980 computers were getting big enough to program useful models rather than just formulas derived from models. Object-oriented programming emerged as a modeling technique.
I was surprised that so many people struggled with modeling. A refrain at the time was, where do objects come from? I wondered, where does your difficulty come from?
I with others explored a variety of big-picture understanding tools: diagrams, crc-cards, patterns, test-first, pair-programming, visualization, metaphor, hypertext, wiki. This became my job within a job: change agent.
I'd been invited to several invitation-only workshops and was getting the hang of being effective in that environment. We started launching our own begetting the Hillside Group and the PLoP series of conferences.
We ran Patterns email list with 500 members. Proof read the Design Patterns book. Launched the first wiki a.k.a. Portland Pattern Repository. Extreme Programming emerged as a set of pattern friendly practices.
Kent wanted XP well defined and not open to revision. Other methodologists wanted their work included. Alistair convened the "light-weight methods" workshop at Snowbird where we had attended a similar oop event a few years earlier.
Magic happens.
The Agile Manifesto website designed to look like a poster and remember the magic. site 
The four phrases of the manifesto appeared like magic. I took a picture. Martin denies authoring them, says it was a group effort. I blur the picture accordingly.
We choose agile as a better description than light-weight which wouldn't sound substantial. We agree to call ourselves the Agile Alliance. I make the website. A leadership battle ensues. I give up the website renaming the page Agile Manifesto.
A plaque commemorates the creation of the agile manifesto.
Dave writes ruby scripts to allow public endorsement of the manifesto. I've reviewed every endorsement to this day. Spam varies year to year but honest endorsements show a consistent pace and discovery experience.
Henrik launches the translation project. I insist on reviewers and translation teams, sometimes a country's first. We discover that the four phrases are hard to translate. They are ambiguous, open to much interpretation. From this they get longevity.