Big Plan Upfront does not work with computer systems:
1) The users rarely know how to express what they need.
2) You don’t have the context needed to understand what they say.
3) Only once you’ve built something do you have sufficient understanding to ask the right questions.

4) Only once you’ve built something can your users see where you misunderstood
5) They’ll have words you think you understand, that have specific contextual meaning to them
6) Neither you nor them will realize until you’ve made noticeable decisions based on those misconceptions.

7) Building is making concrete language and understanding, making visible interpretation.
8) Only once they see where you fail will your users be able to steer you right.

You can’t make a Big Plan Upfront because nobody can readily express knowledge which is innate. They need to see wrong to tell you what’s right.

What the Big Plan Upfront should’ve been only seems obvious in retrospect.