The worst project management I've ever seen was done by salespeople, probably because they're laughably unrealistic about what is actually possible and how fast and how well it can be done, so overpromise all the time thus condemning a project to fail for the start (want to see a guaranteed deathmarch project: go look for any were a salesperson got put in charge), tend to expect that problems get solved with fast talk and change the requirements everytime they speak with customers/stakeholders as if it one could just, say swap the foundations of building half-way done add some more floors on top.

That genuine optimist that comes from not examining something so close and in depth that you start seeing enough detail to spot the potential problems and start grasping the true scope of the task, which is maybe the best quality for selling stuff, is pretty much the worst quality for actually making stuff or lead those who make stuff (in this latter case because of being shit at setting and managing expectations).

Theirs is the last kind of personality you want managing the creating of anything in any way complex.