It's not so much imposter syndrome. It's that research-based graduate experience matters, not in what one learns, but that it forces a person to go through 4 to

It's not so much imposter syndrome. It's that research-based graduate experience matters, not in what one learns, but that it forces a person to go through 4 to 7 years of deeply focused introspection, often on fundamental reality. I suspect similar experience can be gained in a monastery or deep spiritual processes. It's not that PhD is a requirement, people gain this ability in different ways, just it's the most standard way to set aside 5-7 years to focus nowadays. It's not the kind of experience that one can gain from undergrad, or in a regular 9-5. Also when we are older, it's difficult to find the kind of time to do deeply focused introspection on a single topic. Without this process, it's easy to get trapped into superficial learning, and confuse regurgitating factoids with knowledge and insight. The key to do this once again is that instead of trying to learn everything, focus on a singular topic very deeply for a non-trivial amount of time.