It’s a little of both, and like most debates with that answer, it’s not a particularly interesting question. Some PhD-holders were self-motivated before. Other

It’s a little of both, and like most debates with that answer, it’s not a particularly interesting question. Some PhD-holders were self-motivated before. Others learned it at school. Still others were motivated, but unfocused, and had to become disciplined. Everyone who has a strong opinion on the topic is, by definition, extrapolating from limited data. Moreover, even if every single PhD learned nothing in school, it’s still a useful signal if it enriches the pool of candidates who are self-motivated and independent.