The fundamental assumption here is that you are in such a fantastically stable environment that you can spend days planning the next 8-12 weeks, and then that p

The fundamental assumption here is that you are in such a fantastically stable environment that you can spend days planning the next 8-12 weeks, and then that plan is actually reliable. My experience was that maybe 20-40 percent of the plan ended up working (blocked by external factors, shifting market landscape, missed or unexpected work coming up), and then there was a huge amount replanning and time wasted. I just cannot reconcile that 8-12 week cycles is in any way conducive to agile development.