Reminds me of a couple of anecdotes my father told me about his days as a physics undergrad. The first was about a time when he would get somewhat discouraged after studying for hours and making little progress. So at one point he asked some of his really talented classmates (more talented than him) how much they studied and how far they got. They all replied that after hours of studying, they would maybe get through 3-4 pages of the textbook. It was somewhat enlightening for him to learn that even the geniuses couldn't breeze through the material like one might breeze through a dime-store novel.

The second anecdote was about the time my father was getting letters of recommendation for grad school. He got the usual positive letters, each with a couple of paragraphs praising his abilities and intelligence. My father then asked one of his friends (a much more talented friend) if he could look at one of his letters. The friend's letter consisted of a single sentence which contained the words "Nobel prize material". It was at this point that my father gave up physics.

Anyhoo, I guess my point is that grit is of course important, but as other commenters have noted, talent can't be dismissed either. We all have upper bounds, which aren't always as high as we might like.