I have a hunch that impostor syndrome is also a symptom of poor / unempathetic* management - while the implication that there might be something 'wrong' with the individual may or may not be true, I would not be surprised if impostor syndrome could be partially accounted for by a difference in how people process and express prosocial cues.

*unempathetic in the scientific sense; of not being able to fully comprehend how and why a person is thinking and feeling the way they do.

Also, it is probably more important to tell people that personality is malleable and can change - this seems to be one of the root causes of resiliency (C. Dweck et al., 2014).