Though true for a certain subset, otherwise this is not entirely accurate. Impostor syndrome is common among those with extraordinarily high IQs: the highly gifted (3-4 standard deviations from the mean), exceptionally gifted (more so; 5-6 SD's from the mean), and profoundly gifted (in particular; more than 6 SD's from the mean). This is true even for children, who obviously can't be considered to have "made it" or not.
Impostor syndrome is insidious. You know what you know/are extremely fast to spot patterns others don't seem to notice, especially others of your age/experience. But you're just you, like you've always been; and you realize that at any time, someone could call you out for being just like anyone else, because how do you know how everyone else's thought process works? After all, you're just spotting patterns, accumulating data, and winging it. Little do you realize that that proficient/effective pattern-spotting is intelligence (or at least, one measure; measurement tools don't really count creativity, for example, which may be core to true genius, along with a host of other characteristics).
Impostor syndrome is insidious. You know what you know/are extremely fast to spot patterns others don't seem to notice, especially others of your age/experience. But you're just you, like you've always been; and you realize that at any time, someone could call you out for being just like anyone else, because how do you know how everyone else's thought process works? After all, you're just spotting patterns, accumulating data, and winging it. Little do you realize that that proficient/effective pattern-spotting is intelligence (or at least, one measure; measurement tools don't really count creativity, for example, which may be core to true genius, along with a host of other characteristics).