If you read what I said with even a modicum of good will and charity, you'll observe that I recommended that people who don't keep up drop out on their own initiative, instead of being culled by "my own definition of smart enough". I was offering advice, not demanding some explicit policy be introduced and maintained. If you aren't fit to cut it, you'll drop out at some point anyway, and it's best for you if you drop out sooner rather than later: you'll be much happier to have dropped out at 24 than be denied tenure at 3rd tier school at age 38, failing to build wealth and start a family up till that point.

So...not correct.

But how then, do you decide when to drop out? Trying to judge yourself based on the study habits of your peers strikes me an exercise in imperfect information. I would suggest talking to the professor who gave you "emotionally draining" questions and trying to determine what fundamental knowledge you may lack. But perhaps you have more relevant experience you can share.

My experience is that I dropped out after getting Master’s degree, after realizing that while I can graduate and then get a postdoc job, I am simply not able to produce as high quality output as some of my colleagues. In hindsight, and especially looking at some of my other colleagues who didn’t drop out but should have, I made a great decision, and I am very happy to have done so.

I think that telling everyone that they can achieve anything they want is doing them a huge disservice. If you talk to actual grad students or post docs, most of them are actually quite unhappy and unsatisfied at their careers. They constantly fell insecure and unstable, and they in fact are so. This is much less common among top ones, because they quite clearly see that they are ahead of others.

In short, if you don’t feel confident that you can succeed in academia/research, leave before the academia chews you out. If you are confident you can succeed, you are probably wrong, but at least you’ll be much healthier psychologically throughout.