alt Hacker NewsHa ha, but the joke is kind of wrong. While anyone with an MD degree is entitled to the honorific "doctor" that doesn't mean they can legally practice medicine. Becoming a licensed physician generally requires completing a residency program, and the worst students sometimes fail to get matched to the limited number of residency slots.
Yes it's a joke, but to quote some numbers in the US: something like 93% of the US graduates matched to a residency program [1], although the numbers were a lot lower for international students applying for US residency. So if you're talking about US medical students, you have to be in the bottom 10% to flunk out.
The attrition for lawyers is higher, neither has anything on PhDs where the number of "practicing" doctors drops off constantly during and after the degree, and only really levels off when O(10%) of them land faculty jobs.
[1]: https://www.ama-assn.org/medical-students/preparing-residenc...