When developing a project schedule, you can spend days making sure the schedule includes the correct tasks and realistic estimates, but ultimately if the schedule is unrealistic, then the project is going to be in trouble. If the project manager has resources working through weekends and public holidays, when in reality they don’t, there is no way the project will be completed by the expected end date. By communicating a delivery date that is too early and then missing that date can lead to bad perceptions of the team and project as a whole, ultimately the project is labelled as a failure.