The 7th principle of the Agile Manifesto is:

Working software is the primary measure of progress.

Let’s talk what this principle means in real projects, and then get a bit more general as to why it’s good.

How does this principle show up in a real Agile process? There’s a concept we call “velocity”. We assign velocity points for new functionality — not tickets completed! The danger of using “tickets completed” as a proxy for project value is that fixing a bug means closing a ticket. But, fixing a bug means the original ticket wasn’t done right, a.k.a: the software produced wasn’t “working software”. So, if someone spends a day setting up user avatar uploads, they’ve gotten 2 points of velocity. If someone spends a few hours fixing the login system because it was supposed to use emails instead of usernames, they get no velocity points.