Just spoke to a marine engineer contractor, who despairs at the project managers he has to work with. He is making money hand over fist, purely because the PM insists on doing things he has little concept of. He then has to fix the problems, incurring massive extra costs.
His main point is that most of these PMs have never really seen a job done properly, and therefore make, and insist on following, decisions that are often crass in the extreme.
Had a PM promise the customer that the job would be done in 4 days, and when the engineer found out had to inform him that it was a 2 week job. Isn't that page 1 of the project managers handbook? i.e. Ask your engineers before opening you mouth. Beyond belief.