Royce argued that only in small software systems can you do a little bit of analysis then a little bit of coding then be done with the project. He proposed waterfall as a way to build larger software systems.

He argued that these 2 steps were the only direct value steps in developing software - figure out what the problem is then write a little code to solve it - he acknowledged this was the perfect ideal since the two steps directly benefit the output product but he also argued this can’t scale to larger systems.

So various analysis and testing steps were added (none of which directly contributed to output, all were drags or costs on delivery - with the idea that they catch more problems earlier thus paying for their overhead), with feedback between them to catch earlier errors, and thus waterfall.

The agile mindset revolves around the idea that the other steps added are BS. The agile mindset solves for the impossibility of a 2 step analysis then code process at scale by reducing scale. It does this by using very small iterations and removing handovers between different parties.