It looked like 8 months of work. It might be finished by year-end. Fatal mistake: we gave a "number". Year-end.
We did due diligence, investigating source applications, data marts, subject areas, etc. And, the client delayed their decision-making process.
After the investigation, we created a detailed estimating model. We didn't create a waterfall schedule. Instead, we defined a typical release and sprint structure and a backlog.
The Unacceptable Revision
We wound up with 9 months of work, beginning next month.
Our sales person was appalled -- shocked! -- that we could no longer make year-end.
"Duh," we said. "It's a month longer, starting three months later. What do you want?"
"We can't tell the customer that," the sales person said.