A popular genre of academic story involves This One Student. This One Student defied all expectations, succeeding when you never would have imagined it. Therefore, we should assume that everyone can totally succeed at whatever they're currently trying and we shouldn't discourage them.
Well, no. While I do grant that most people can, with sufficient time and effort, do most things to at least some level of competence, it does not follow that a person with precious little preparation can succeed in the class in which they are currently enrolled. Maybe they need to go back and make up deficiencies before attempting this course of study. It's insane to think that they should be able to remedy any and all gaps on the fly. There's a reason why courses have prerequisites.
If a student is showing fundamental weaknesses in, say, algebra, they can still learn physics, but they should probably spend a substantial amount of time first remedying those gaps in algebra knowledge. Yes, yes, they passed a math placement test that was approved by people who answer to officials who need a certain level of throughput. Yes, they passed an introductory calculus class taught (and, more importantly, graded) by somebody who has no job security and answers to a system that wants to see students pass classes. That does not mean that they actually know high school algebra, as is demonstrated to me on a daily basis. Most of these students will flounder for years, fail and repeat classes, and eventually rack up enough partial credit to pass and graduate.
Nonetheless, from time to time we see This One Student who starts off doing terribly in algebra but goes on to do remarkably well. That's wonderful when it happens, but it's rare. It is inhumane to think that everyone should be encouraged to invest prime years of their lives and take on substantial loan debt in the hopes that they'll replicate This One Student's success story.
Moreover, it is often the case that This One Student has some unique advantage or compensating factor that we cannot easily replicate. Sometimes it's a special personal factor that couldn't help them with algebra but could help them succeed in an internship that gave them the motivation to push ahead. Sometimes it's an extraordinary personality characteristic or raw talent.
I was recently talking to somebody who started telling the story of This One Student, and it turned out that the student had served in an elite military unit. (I rarely believe claims that somebody served in an elite military unit, but the fact that This One Student pulled off an extraordinary feat suggests a level of self-discipline and work ethic consistent with their claimed military background.) Well, your average student does not have that kind of dedication. In fact, even your average soldier, sailor, airman, or Marine does not have that level of mental tenacity.
They also told the story of This One Other Student who had the immigrant work ethic required to spend half the year working full time in shitty jobs, saving money for college, then attending college full time during the other half of the year. Well, most students do not have that immigrant work ethic. Nor do they have the humility and self-knowledge required to accept that they'd be better off EITHER working full-time OR going to school full-time, rather splitting their time and failing at both. You could say that it's my job as an older, wiser mentor to help them see that, but I can't even get most students to follow instructions regarding algebraic steps, let alone major life decisions.
There are few tales more destructive than the tale of This One Student. It gives us endless optimism, which is the bane of useful advice.