How hard is it to get into grad school and do a PhD

I didn’t last very long in grad school. My impression is that it’s not really about how smart you are, it’s more about your organizational skills, your research skills, your ability to focus on reading a whole helluva lot of dry content and then write papers way longer than anything you wrote in undergrad, your executive functions (general ability to just get stuff done), and how hard you’re willing to work at it. That kind of thing.