Negative slack tends to increase. In case of doubt, make it sound convincing. No matter what stage of completion one reaches in a project, the cost of the remainder of the project remains constant. Leaving is much more difficult than entering. Expenditures rise to meet income.
Manuals expand to fill all the allocated shelf room.
Under the most rigorously controlled conditions, the experimental apparatus will do exactly as it pleases. They won't work. If computers get too powerful, we can always organize them into a committee. That will do them in. Any given program, when running, is obsolete.