At the time I had that idea I got the impression that some of the people around me were leaning too heavily on what I was calling the "epistemic lens," where your perspective on people is primarily based on their beliefs. I think this is mostly unhelpful, e.g. it can cause people to be snooty about religion for what I see to be no good reason. I think an "instrumental lens," where your perspective on people is primarily based on their actions, is much more helpful. In general I'm a fan of instrumental rationality, rather than epistemic rationality, being the more foundational thing.