Short version: when designing new software, you don't have its architectural picture in the beginning. So when starting from scratch, the architecture shouldn't be screaming, but rather, it has to be non-committal/non-speculative to allow wiggle room for the future. (How to achieve non-committal architecture is the biggest topic I'm interested in, and I find 1 good tactic every few years). Specifically, the architecture should ephasize entry points and outputs. That's exactly what frameworks like Rails provide. You go by entry points until some sort of custom architecture starts emerging from the middle, which is when it can slowly begin "screaming" over time.