Building Software is unpredictable. Because of this inherent unpredictability, you should never constrain both a ship date and a feature list for a projected release. Not even adding more people to a project will get around this law. As Fred Brooks famously taught, “adding manpower to a late software project makes it later”

This a hard, inconvenient truth about software, and it makes many activities very difficult (marketing future releases, negotiating contracts, creating product road-maps), but ignoring it causes conflict and dysfunctional behavior.