Even if you’ve tried to do a good job estimating, planning, and scheduling, you will still encounter sponsors, managers, and team members who will game the schedule. Your job is to bring those game players back to reality. But first you need to recognize the schedule games.
All sponsors and managers will push back against your schedule at some point. These games occur even when you’ve created a reasonable project schedule. Many of the ways in which they push back fall into easily recognized patterns. The better you are at recognizing the game they are playing, the better able you will be to steer the project to a reasonable outcome.