> The way anything actually gets done is by initially being overly optimistic (...)
I don't think so. At most, planners plan for the happy path and then add slack to help them manage expectations. Sometimes stuff emerges and projects adapt. Sometimes your slack covers it, sometimes it doesn't and you get delays and extra costs. That's a Project Manager's dish of the day.
> then lock it in via sunk costs
You're presuming that clients are oblivious to issues of delays and cost overruns, and the negotiation stages don't include accountability specifications.
I don't think so. At most, planners plan for the happy path and then add slack to help them manage expectations. Sometimes stuff emerges and projects adapt. Sometimes your slack covers it, sometimes it doesn't and you get delays and extra costs. That's a Project Manager's dish of the day.
> then lock it in via sunk costs
You're presuming that clients are oblivious to issues of delays and cost overruns, and the negotiation stages don't include accountability specifications.