Grit is useless without focus. Calculus, and math in general, provides focus: it cuts through the BS.
We aren't living in an era of people suffering because they did too much calculus they don't need.
We are, on the other hand, living in an era where people are lied to, fooled, prayed upon, and duped everyday, because they can't understand math.
We also live in an era where people could do amazing things, even as amateur hobbyists with some math and science knowledge, but are drowned in BS doom-scrolling, binge-watching of crap, and the like...
I was just reading Sir Walter Scott's Waverley where he suggest that this is the main reason for a classical education as well:
> Edward would throw himself with spirit upon any classical author of which his preceptor proposed the perusal, make himself master of the style so far as to understand the story, and, if that pleased or interested him, he finished the volume. But it was in vain to attempt fixing his attention on critical distinctions of philology, upon the difference of idiom, the beauty of felicitous expression, or the artificial combinations of syntax. “I can read and understand a Latin author,” said young Edward, with the self-confidence and rash reasoning of fifteen, “and Scaliger or Bentley could not do much more.” Alas! while he was thus permitted to read only for the gratification of his amusement, he foresaw not that he was losing for ever the opportunity of acquiring habits of firm and assiduous application, of gaining the art of controlling, directing, and concentrating the powers of his mind for earnest investigation—an art far more essential than even that intimate acquaintance with classical learning which is the primary object of study.
But I think the above poster has a decent point, in that there are many places where you can train your brain to focus that will also provide you with skills that are more useful for most people. For instance, I'd say statistics, combinatorics, and probability will be more useful to most people.
Of course, if you're in a field where you need to learn calculus, then you need to learn calculus, just like if you're in a field that needs differential equations or topology, you need to learn that. But that's a small segment of the population. I've studied calculus for fun (and differential equations as well), and enjoy it, but have never once found myself running into a use for it in the real world.
Programming, music, art ++ isn’t as good as calculus on this.