Regarding success, it's all in your mindset
Twenty-five years ago, I taught part-time for a postsecondary school in southeast Iowa. The reality of working as an adjunct professor is a mixed bag. The pay stinks. The work, on the other hand, can be bliss. It was bliss for me because I, though seriously underqualified, was teaching an introductory philosophy course. No such course could fail to include the teachings of Aristotle (I have a painting of him hanging in my office) and, I was amazed, as a poor but ardent disciple of the founder of the Lyceum and tutor of Alexander the Great, that I was getting paid at all for doing something that I loved.
Teaching Aristotle was particularly enjoyable because I used videos of one of my educational heroes, Mortimer Adler. These vintage vignettes were somehow enhanced by their black-and-white format, grainy images, and poor audio quality. In one, perhaps the best of the best, Adler explained that for Aristotle the happy life was the good life and that you could only tell whether or not a person had lived a happy life at its end. To attempt to judge it earlier than that was like trying to judge a cake's flavor while it was still baking in the oven.
On this point (well, OK, on pretty much every point), Aristotle's logic is impeccable, Adler's unassailable. You can't know the true value of something if you don't consider the long term, even the longest relevant term.
(There are counter-examples, though. I was once asked long ago in a superintendent job interview in Iowa about my long-term goal. Offered, by the nature of the question, only one response, I responded 'to get to Heaven.' I didn't get the job.)
The long-term matters a great deal in education. We all know people who 'peaked' in high school, who were popular and attractive and successful in the classroom and the athletic field and pretty much everywhere but who then couldn't translate that success into much after they shuffled off the commencement stage. We all know people who can hardly remember what the letters B, C, D, and F look like because they've never seen them on their assignments or report card. But somehow, when the grades stop, the lack of unambiguous criteria for success flummoxes them. Not all, not even most, but some.
One possible explanation for this is offered by Professor (full-time not adjunct) Carol Dweck of Stanford. In her book "Mindset," she reviews two approaches to education and other goals that people operate from in their lives. One is the fixed mindset, the other the growth mindset.
A person who lives through the lens of the fixed mindset assumes that his intelligence and abilities are fixed. If he is good at something, great. If not, there is little he can do about it but pursue other things, things he is good at. The problem with this frequently emerges after high school when a high performer, perhaps for the first time, discovers that some academic subject, some life's goal, some career requirement, is difficult. Having a fixed mindset, he throws in the towel. Faced with enough of these, he is forced to readjust his understanding of his place in the world and accepts a smaller, less enlightening place therein than his abilities actually justify. He is trapped in a cage of his own making; of, in fact, his own imagination.
A person with a growth mindset, however, assumes that she can be good at anything, with sufficient exposure, study, and practice. Being lousy at something isn't the end of the story, but the beginning. What she is bad at, in fact, can be a sign not of failure but opportunity, a great undiscovered country waiting to be explored through earnest effort. Such people may not have been all that successful at high school for whatever reason, one of which is the possibility that they were pursuing learning rather than grades which could be safeguarded by course selection and other occasionally subversive techniques, but then began an upward climb in postsecondary study, career pursuits, and personal growth. And we all know people like that as well. (A former college roommate of mine once complained of getting a B in a course he almost never attended because it indicated he had worked too hard; he was only after a C. Today, he is a highly regarded full professor of economics and finance. I'm not sure whether he always had a growth mindset or developed one in grad school.)
But the point remains. If we really do want to be successful — and we all do or at least should — we need to look at the long-term, beyond the next assignment, past the coming grading period, beyond even the day we earn our sheep's skin (diploma), to our ultimate or at least more ultimate goals. Doing that can be immeasurably facilitated by a growth mindset.
It may, indeed, be the secret to success.
As to the secret of happiness, don't bother looking for that here. But you might want to consider picking up a copy of the Nicomachean Ethics.