Or as a good friend told me when I was starting my PhD: "those of us that finish our PhDs are not the most intelligent, but the most stubborn "
Or lucky! I had a great time during mine because my advisory was amazing. However, my cohort mates, many of whom I'd say are much smarter/intelligent than I, got stuck with terrible mentors.
As my friend said of doing a PhD, “you learn more and more about less and less until sooner or later you know nothing at all”