We assume that software is so simple that its development can be easily planned from the beginning to the end phase. As all project variables (like scope, size, cost, risk, and the like) can be predicted during the initial phase, we assume that upfront big planning is possible and enough. In fact, planning should also evolve along with the requirements.

To confirm this, the Standish Group Chaos Report 2015 segments the result of Agile and the Waterfall model based on software projects across sectors between 2011 and 2015. It clearly indicates 39% of Agile success versus 11% of Waterfall against all-sized projects. It comprises of Agile split of 18%, 27% 58% against large, medium, and small projects respectively.