If you wonder why projects you are on do not succeed, or make significant progress, look to your project members and stakeholders.
Determine the slowest, least engaged, or least motivated. Map your project schedule to that person’s ability to deliver. Then convince management that that project pace is feasible.
You will spend less time changing deliverable dates, explaining to project sponsor why you are behind schedule, and frustrating your development team due to late-breaking, must-have functionality.
If your project management team is the cause of issues, change jobs.
This guiding principle is useful in personal relationships as well.