Everyone agrees what it should look like long before anyone agrees what problem it solves.
The people writing requirements, drawing screens and building it are each working from a different picture.
The quick decision made in week three is still there, and now four other things depend on it.
Problems surface the week before launch, when they are most expensive to fix.
Logins and permissions get retrofitted once the product is built, which is the hardest time to do it.
It ships before anyone has worked out who gets called at 2am, or how you would undo it.
What their job is, what they are answerable for, and what they need in front of them to do it.
We take the tangled parts apart a piece at a time, while the thing keeps running for the people who depend on it.