IQ provides potential, not results.
A person of below-average IQ, no matter how hard he works, will never be a stellar performer in occupations requiring high IQ.
OTOH, a great many high-IQ people spend a lot of their time and energy bitching about the fact that people they work with who aren’t as smart are doing better than they are. Don’t believe me? Attend a Mensa meeting.
Think of it as height. A very occasional person under 6’ might succeed in the NBA, but in general those who succeed are above 6-6. The taller they are, the more likely to succeed. That’s because you can teach the skills, but you can’t teach someone to be 7-2.
Again, a 7-2 person unwilling to work hard would not succeed.
You’re right. High IQ people are more likely to drop out of high school than average students. Unfortunately, being able to learn things quickly sometimes keeps individuals from gaining the character that is also required to succeed.
I have also seen people who knew they were not as quick on the uptake work very hard and surpass others who theoretically should have run rings around them. They made up for (actually, overcompensated) for their deficits by working hard.
In the long run, being willing to put out the effort and not just rest on one's laurels is the most valuable in relatively ordinary life.
Sure, If you have a wee bit of trouble with nuclear physics, you might not get the top research position at CERN, but there are numerous other (often prosperous) niches to inhabit.
You probably could do well in the NBA if you can turn fast and shoot well, and while there is a definite height preference there, the little guy would have the same maneuverability advantage a two-year old has running from an adult. (Try that some time, they can turn on a dime and give you 9 cents change.) Combine that with the ability to hit quickly, often, and accurately from anywhere and if they could get a chance to show their stuff (past the height bias), they might do well. But littler guys won't put the effort in because they realize the height bias exists, and go off in other pursuits.