<p>I think for physics there is a certain minimum level of intelligence that you must meet to be successful, but beyond that, I think your success is determined by hard work and creativity. For example, when I took honors physics my freshman year of college, I put in a lot of work, always going to lecture and taking notes and spending a significant amount of time on homework. Not only did I do problems, I also really made an effort to understand things rereading derivations in my notes and textbook until I could see the logic behind every step. There were some other people who by comparison just skated by and it appeared that they were able to do well without putting in much effort. Sometimes thought that they felt superior to me because I put in so much effort and this made me feel like I wasn’t smart enough to do physics. I was probably also somewhat misled by appearances. It is possible that these people put in more work than they said they did or that they were not doing as well as I thought they were, but at the time I felt very discouraged.
Fast forward to the end of junior year. By this point in my academic career I have been very successful in several graduate classes, in research (I am currently publishing a paper in a theoretical field), have received several very significant awards, and have great relationships with my professors, a few of whom will be writing me letters for grad school. However, many of the kids who I thought were so much smarter than I was have burned out. Because I spent so much time studying in my earlier courses, graduate courses have been very straightforward for me since I understand concepts beyond just doing problems and have the ability identify relationships between topics. For others, upper level and grad courses have been a huge challenge, with one person saying that our undergraduate curriculum had not prepared him to take grad courses. Another person who never went to class the first two years is now discouraged from applying to physics grad school. So the moral of the story is that physics is not a race, it is a marathon and you need to work hard to be successful in the long run.</p>