The traditional plan-driven projects are based on the traditional “iron triangle” of Time, Cost and Quality. All requirements have to be accounted for in the requirement phase and then the project is planned around the expected features to be delivered. The features are the first ones to be fixed, afterwards an estimation of time and costs in delivering those features is drawn up.
The Agile mindset, on the other hand, is to fix time and cost to manage a variable scope. This leads to the ability to hit deadlines both in the short and long perspective. This way it’s easier to focus on features that build value and to avoid building features that never will be used.
Remember Pareto’s principle – the old 80-20 rule. Vilfredo Pareto, an Italian economist, observed in 1906 that 80% of the land in Italy was owned by 20% of the population; he also observed that 20% of the pea pods in his garden contained 80% of the peas. This is how he came to formulate this principle. In business, people say that “80% of your sales come from 20% of your clients”. So wouldn’t it be great if you could avoid building features that will never be used?