|Do you know where your variables are?|
I think (although old) the waterfall methodology of developing software is the best one.
Sorry, but you just outed yourself as not having a clue. The waterfall methodology was never any good.
Just maybe, if the designer is (re)designing his 4th or 5th data entry system, (or other simple, linear flow, data in-process-results out system), and the project is small enough that one person can envisage and retain the entire systems flow in their head. Then, just maybe.
But for anything that involves leading edge development, or more than one man can keep in his head at one time, waterfall is useless. And the cause of many billions of wasted £/$/¥ over the past 40 years.
Waterfall lives up to its name: once you're over the edge, there is no way but down. The smallest change in requirements; or misinterpretation of those requirements; or miscalculation regarding scale, speed, or technical feasibility; and the end result is a dog of a system that condemns your users to perpetual pain; your programmers to constant make-do; or the project to cancellation. Or all three.
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.