People, in PhD programs, in post-docs, leaving science, is an ongoing discussion, here and elsewhere. The causes of leaving engender passion and righteousness, and self-righteousness. There are manifestos, diatribes, and not some small amount of sadness.
Everybody agrees that there are probably not enough (meaning enough for everyone who might want one) jobs (meaning the preferred employment, in these discussions an academic professorship) and support (meaning an NIH R-level grant).
Part of the discussion I've come across is trying to separate out the legitimate selection mechanisms from the ones that are socially imposed. The latter are excoriated for not selecting "the best" of science. I think all right thinking people agree that the "this group is stupid and can't think" arguments are prejudices and entirely without merit. Beyond that, we enter the realm of more subtle concerns. Being subtle means only that the roots and branch implications are not immediately apparent, not that there is defensible value in those concerns. I find I quickly get confused when I read these things.
In other fields, that a sorting and selection process occurs is taken for granted. No one expects that every high school athlete will make it in the pros. Artists, visual, dramatic, performance, are all too aware of the difficulty and challenges of success, and often the mind-numbing finality of the "day job for just a while".
A small aside, but probably quite relevant in the long run: One of things that interests me is that in art, visual or performing art, some of those forces, the bad forces that keep people out, or try to keep people out, or even are just making it very difficult to succeed, are exactly those forces that shape the art and make it compelling, valuable, worthwhile, important. Stories told in a vernacular, stories told in the language of the oppressed, may not have been high literature once upon a time. But the power of those stories, told in those languages, move us, change us, make us more than we would have been. We come to recognize, society comes to recognize, art in a new form, art that grew out of efforts to keep the artist away from creating. We may argue today about this modality or that, but history shows us what we were foolish about 100 years ago. Stravinsky, Gauguin: does anyone doubt their art today?
In some ways, sport as an career choice is more clear: it is competition. Winners tend to be very obvious. Better is judged by winning. And that competition, the mental rigor of that competition is part, perhaps a very large part, of what drives individuals towards success. Art and science are, again, more subtle. If you lose a tennis match to Serena Williams, you know it. When does an artist decide that they cannot live on beans and rice and in an apartment with less desirable urban roommates, human, insect and rodent?
Is science different from art? In the discovered/undiscovered, there are some synapomorphies of human endeavor. But for every Stravinsky who endured and persisted, there was undoubtedly a woman of color, a person with disabilities, a working class individual who never got the opportunity to leave the factory in which they worked, whose music we will never know. There are people who did science against the odds, but also probably lots more who might have changed our lives, people who never had the right combination of resources and luck to be what they could.
So, what is our responsibility, aware that we are of their potential existence, to young people today who might be scientists (let alone artists)? We all decry those dystopian novels where there are tests and trials and some Greater Authority makes the decisions. But we are also not happy with a random river of time and chance throwing greatness up on the banks of society.
Had we but the resources, we would give every child the opportunity to explore and be educated and find what they can and will do. But large swathes of the world don't have enough food and health care, let alone basic education. The anti-dystopian novel (think "The Giver") where the young rebel escapes the deterministic society and goes off to find what they are and Make A Difference is as unrealistic as the utopian visions. Aside from value as parable, these stories are disturbing. They are often framed as genius, of one sort or another, against the world. It’s often only the protagonist who escapes, and the Rosencrantz and Guildensterns of society, perhaps not genius, but perhaps creative, are left behind. What happens to them?
[Another aside, while there may truly be geniuses, and “top of the game” scientists, it is not a binary, bimodal distribution. It is not. There is not the .1% of incredible science, and the rest is trash, as has been asserted by many people. It is not normative and transformative science. The reality of scientific effort, product, output is far, far more subtle than that. Alas, another post].
If we all truly, really, deeply and meaningfully cared about that lost genius, let alone the good but not quite genius, we'd stop doing what we are, which likely has minimal impact on the lost children of human society. We would become activists and teachers and do something to effect change so that those children would have the chance to realize their potential.
Ah. But we have our rationalizations: I am better at doing my science than I am at organizing. I can do more good teaching here than I could in South America or Africa or rural anywhere without education for female children, non-binary children, children with handicaps and differently colored skin and eyes. If I make money, I can give it others, and that may do more good.
So we persist and do the small things that we can. Changing the world is hard. In my youth, I surely thought everyone who wanted it deserved a kindly mentor and a full stipend and a chance to be a scientist. I am unsure that that statement is false. I am also unsure that it is true. While many things have become clearer to me with age, this is not one of them. How do we choose who gets to be a scientist, an artist, even a doctor or lawyer or candlestick maker? Right now, the world is out there, and people, young people with dreams and wants, go at it, as best they can, with the tools they were given as children. The world while sometimes helpful and sometimes cruel, is largely indifferent to their efforts. Unlike sport, there is no ultimate World Series to determine who gets to be the best. There is no Final Four of college or grad school. We try, and the world throws its stochastic self at us in the form of mentors and opportunities and people we meet and talk with. So we teach them resilience and persistence and help in the ways we can.