" Marginal gains is not about making small changes and hoping they fly. Rather, it is about breaking down a big problem into small parts in order to rigorously establish what works and what doesn’t. Ultimately the approach emerges from a basic property of empirical evidence: to find out if something is working, you must isolate its effect. Controlled experimentation is inherently “marginal” in character. "

― Matthew Syed , Black Box Thinking: Why Some People Never Learn from Their Mistakes - But Some Do