The scope is agreed with one person, and a second person turns up in week three with a requirement that was obvious to them and to nobody else. That is not their fault, and it is why the scope names who agreed it.
The export arrives with a field missing and nobody notices until the output looks wrong, which is week two rather than week one, because you cannot see a missing field until you need it.
Somebody assumes three weeks means three weeks from signature. It means three weeks from data. Those have been six weeks apart, and the gap was always somebody's holiday.
And the person who has to own it afterwards is usually not in the kickoff, because they are busy. We now ask for them by name in week one, because handing a working system to somebody who has never watched it break is how it stops being used by month four.
What changes
Each of the four is in the scope before it can happen: who agreed it, the field check in week one, the clock at data, the owner named.