Project Managers are responsible for "Making it Happen". There are many promises in any Project Plan.
Project Managers typically work to Budgets and Timetables inherited from others. Keeping Promises others have made on your behalf starts with an inherent problem - you are not necessarily committed to it. In fact, what most employers want out of a project manager, is "Yes, I can" - whether or not they can or will. Each milestone they are trying to fulfill is a promise to deliver a mini-project to a time, budget and quality.
When projects are larger than one person, the project manager has to keep promises over which he or she has no direct control, i.e. the work of others. It's hard enough when you are doing the work yourself, much harder when you are trying to inveigle others to meet third-party promises on your behalf. And what if the only person getting a bonus for meeting promises others have made is the project manager? Who in their right mind would work more than the minimum in those circumstances? And would you want people not "in their right mind" doing your work anyway?
Perhaps "handling people", as in "supporting, motivating and listening to", is the chief skill of the project manager. After all, shuffling schedules can be done much better by using software. So the most obvious improvement for projects is having the project manager and his whole team create the Project Plan and set their own goals. For extra credit, tie the outcomes - both positive and negative - to meeting the promises made. Skin in the game and real consequences for everyone.
What of the "Back Office or Professionals' Performance Paradox"? The more skilled the performer, the easier the performance may look. All those professional sports stars we see on TV such as drivers, footballers, tennis and golf players. Can't be all that hard, can it? The drivers are all going around at about the same speed and the scenery just passes by. However, on your couch you don't get to feel the G-forces, experience the sound, or feel the terror and exhilaration of almost crashing.
In everyday professional practice the best practitioners make fewer "mistakes" and things work out much better for them for many reasons - not only because "practice makes perfect" but also because prior preparation and planning are also a part. Good practitioners get a task and "Get it done". Great practitioners get given hard tasks and perform them quickly and seemingly effortlessly. To an outsider, inputs (effort and time) are all that is visible.
Poor practitioners fight bravely with every task. Even the simplest job becomes a marathon and "bigger than Ben Hur". But to the outsider, those putting in the most work and experiencing the most problems must be "better" and working "harder", mustn't they? In the end, uninformed employers will wonder if they even need a "professional" who never seems to be rushing and might appear mostly to be "doing nothing useful" - like reading, planning or studying!
If you make the job look easy and your actual performances aren't visible (Back Office tasks), your employers may think your work is worth little and can be done by anyone (i.e. someone who costs much less). This is not an original observation in Computing/IT. Jerry Weinberg documented this in 1971 in his landmark book The Psychology of Computer Programming.
Which of course sank almost without trace.
Hope this is useful/interesting.