You make a valid point about the need for hypothesis tests. If it’s possible to clearly verify a root cause with data or observation, then you wouldn’t need to conduct a hypothesis test. We chose a simple example in order to make the topic more digestible to people who might otherwise avoid the topic. The other reason to use a simple example was to show that it’s actually not that hard to conduct Hypothesis Tests. If you already have the data, it’s a few short steps to run the test. Even if the data makes the root cause obvious, running a hypothesis test gives people practice and lets sponsors and leadership know that you’re proceeding with hard proof. When there’s money, time and momentum at stake, it can be worth it.