Megaprojects: Over budget, over time, benefits less than projected over and over again

[dismal]

It applies to everything involving money transfer, you are assumed and expected to llie exaggerate.
If you are not doing that they would still think you are doing that.

In the world I inhabit engineers are expected to hit their estimates so they are conservative. Wildly overrunning a budget is career limiting.

In the political world, where most of these megaprojects reside, there is a tendency to wildly overpromise to get the project approved and a general failure to hold the overpromisers accountable that reinforces the behavior.