Although talent may be a crucial element on the road to fame, it is difficult to succeed without a highly developed work ethic.
We can tell that "fail" has become an adjective because it can be preceded by the quantifying adverb so, as in "I'm so fail." [Cf. I'm so happy (adj.), but *I'm so student (n.)].
Q: As an SAT writing instructor, I am intrigued by your Grammar Myths page, which debunks the rule that "none" is always singular. Since the College Board follows this rule, we have thousands of students learning to write sentences like “None of the chickens is hatched.” What do you think about that?