"Sure, engineers can "work" with that, which means they have to implement AND design the product as they go. Which usually ends in a mess for all parties involv

"Sure, engineers can "work" with that, which means they have to implement AND design the product as they go. Which usually ends in a mess for all parties involved." IMO that can work as long as engineers are experienced enough, and expectations are set on both sides. PMs will have to accept an iterative process where people gotta keep refining to get to an ideal state. And Developers will have to accept that "iterative" means you'll constantly have to re-do work or throw away stuff. But if either side can't accept that, you'll end up with a mess alright.