I agree with the author that you as a worker have to sometimes say no to certain things. You want to be able to finish a task based on a realistic goal. You do not want to say yes to your manager for a task knowing that it will probably not be finished by the right date. Here it is better to say no so that the managers will be able to work around the date. In software development you would rather spend a little extra time to get the software to work correctly rather than rush into releasing a product that barely works.