> implement following conservative assumptions, revisit and refactor aggressively > The latter being vastly more effective at honing good design because more decisions are made in retrospect.

Only if people actually do that.

I've joined a project where a design doc should've been written before the first line of code (as per the agreed upon dev process). Developers disregarded that and yolo'd their way to a first prototype. No documentation whatsoever. Then someone else was tasked with writing a design doc for that big ball of mud. You can imagine how that went.

I've joined the project only much later. At every corner I'm dumbfounded by the "design decisions". Refactoring now is a herculean task and kept to the minimum required.

I'm certainly not advocating for waterfall-like "make a plan and stick to it no matter the cost". But looking at the requirements and drafting a coarse design from those goes a long way. At least you can get idea if whatever you have though up is in agreement with the requirements.

Treat the design document as a living document. Do a coarse draft first. Implement. Refine the doc with stuff you've found out, ditch the stuff that didn't work. As a bonus you get a relatively neat on-boarding doc for people joining later.