Comment by fallinditch

Yes. I took over the project management of a job where the previous project manager had spent a year planning it out, but development had not yet started. The client was furious, understandably.

I abandoned the plans from the previous PM and discussed the job with the developer who ballpark estimated that the work would take 2 months. After a quick analysis I adjusted this to 14 weeks.

But the account manager thought this sounded too long and insisted that we plug everything in to a Gantt chart, define the shit out of everything, map the dependencies, etc, which showed that the development would only take 6 weeks.

The project ended up taking 14 weeks.