The best players all think they will be 1 and done...., until they aren't. Personally, I give favor to the ones who think they are that skilled. All of these ones have to make huge adjustments once they are in a college program. The speed of the game causes the most regressions for these HS players who have come up through the AAU ranks. Also, most of these athletes are woefully short on fundamentals and strength that are requisite for making an NBA team, and many wind up either out of basketball or in the "D" League trying to make a team. The success rate in making the NBA and staying in the NBA is rather low.
Many to most are shocked to learn that there happens to be a plethora of players that are just as skilled, that are stronger, and possess very legitimate quickness that they were not expecting and that if they want to realize their aspirations in regard to the NBA they have to address these shortcomings, and most times that means staying in school until they have the requisite skills required. We have Bacot & Caleb as examples just from our team. Both declared that they would be one and done, and there are too many other examples that I can add, but I think you get the picture.
I am not saying that no HS players do not have the skills to move on after 1 year, I am just saying that more than likely that those pronouncements by high schoolers are mostly wishful thinking, and by far, most who do, do not fare well for any length of time. While we can point to some successes, the percentages of success are quite low.
The reason I favor players with the 1 and done mindset is that they have extreme confidence in their abilities on the court and confidence in themselves is not something that has to be continually pumped into them by a coaching staff, even if they find out that they do not have the requisite skills required to move on to the next level.