The people who use the building-construction metaphor for software seem to think that the estimates you get from contractors are dead-on accurate. They aren't, for this reason . In fact, no contractor I've ever heard of will give you an estimate. They'll either go T&M, or give you a _bid_, which is usually 2x or 3x their (internal) estimate. They're not idiots.

Source: x.com/allenholub/status/1817327805853745637