A/B testing is a powerful customer-driven quality practice, which allows us to test a variety of implementations and find which works better for customers. A/B testing provides actual data, instead of the HIPPO.
The folks at Twitch found that the users in the test cell had higher engagement than the control group. They found that this higher engagement came from factors other than the new experience, which might cause a cognitive bias in their results. Factors like the Hawthorne effect and new users break the randomness for the experiment.
They adjusted the data to reduce the impact of these effects, and provided a great case study on how they did it