I find that many of the PhD students who struggle are not prepared for the mostly self-driven nature of the pursuit, and have not had enough work experience to know how to choose a supervisor.
The statistics support this: a majority of the PhD dropouts are students straight from undergrad who performed well academically, but have never had work experience.
Finishing a PhD is as much about selecting a good PI as it is love of the science. Anecdotally I've seen many great students struggle because of lack of support from their PI, and many "worse" students do extremely well because they chose a terrific PI who builds a support system around their students so they almost cannot fail.
The statistics support this: a majority of the PhD dropouts are students straight from undergrad who performed well academically, but have never had work experience.
Finishing a PhD is as much about selecting a good PI as it is love of the science. Anecdotally I've seen many great students struggle because of lack of support from their PI, and many "worse" students do extremely well because they chose a terrific PI who builds a support system around their students so they almost cannot fail.