manager is being asked to develop an initial estimate for a large-scale project to get additional organizational buy-in. That does not mean that the agile project manager should throw out numbers ad hoc.
Even though, Malcolm Gladwell  coined the phrase "don't think, blink!" where he believes that spontaneity could lead to better decisions, others believe that even intuition needs some time to put a very complex situation into perspective, a situation we commonly describe as "I will need to sleep on it." This allows the decision maker to let the information sink in and get more comfortable with her own decision.
Experience Affects Intuition
The intuition comes from experience and puts the past into the context. In agile project management, we learn incrementally— sometimes the hard way— during a sprint retrospective. But it is exactly in these retrospectives where this context for future decisions is established. Instead of learning project by project, agile project managers learn increment by increment.
With this approach, we improve the context of our inner voice steadily and increase the quality of the estimates quicker than with traditional approaches. Sources of that context could be that too few resources were allocated to an iteration, easy features turned out to be more complicated than expected, or, of course, the price to develop a feature was beyond the initial estimate.
Yes, these were issues during the past iteration and might have caused tremendous trouble, but because of them we established more context, essential for future decisions. This is particularly important for agile newbie's. Think about it: requesting a price tag for a project, or even just a single iteration, from an inexperienced project manager seems silly, doesn't it? Even if the newbie had a complete breakdown of tasks laid out as a "master plan," someone's inner voice would be still heard during the estimation exercises.
We call these methods Expert or Wide-Band-Delphi , but they might be representations of a team member's inner voice. So even if we do not have these detailed plans, we could apply the same techniques.
So is our industry aiming for these scientific approaches only because we are part of broader engineering disciplines with a strong background in math and physics? What would be the most likely first question from senior management if you presented an estimate of five to seven million dollars for a new project?
"How did you come up with this number?" Answering "My intuition tells me that" might not be sufficient for your audience. These psychological studies indicate that we see feelings and emotions as dumb and therefore try to use a scientific approach to rationalize and prove our intuition. But, in reality, they seem to lead to better decisions.
From my own experience, I recently had a general contractor look at a job at my house. He entered the house and even without looking at some of the rooms, he threw out a price that I thought was very quick. Later, after the project was completed, I asked him how he came up with his estimate. He simply answered, "based on my experience, year built, and size of the house."
After I noted that he hadn't looked at all the details and even some of the rooms, he added "Well, there is always something you don't know until you open the walls." After project completion, it turned out he was dead-on. It was a successful project for both of us. I am sure, however, that his personal retrospective for my project will influence the next homeowner's estimate one way or the other.
Where Do We Go From