" With these caveats in mind, then, RCTs offer a powerful method of establishing rigorous tests in a complex world. Handled with care, they cut through the ambiguity that can play havoc with our interpretation of feedback. And they are often simple to conduct. Take the example of the redesigned website mentioned earlier. The problem was in establishing whether the change in the design had increased sales, or was caused by something else. But suppose you randomly direct users to either the new or the old design. You could then measure whether they buy more goods from the former or the latter. This would filter out all the other influences such as interest rates, competition, weather and so on, and reveal the hidden counterfactual. "

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