There's also a useful version of such critical remarks which can be made. One wants two things: (a) remarks which help people understand their own potential better; and (b) remarks which help people better understand what's involved in working in a particular field.
I was a good student (in the sense of: I got good grades). But people make judgements on many bases. The academic advisor was well intentioned. But I didn't fit his model of what a physicist should be, in ways I now realize were irrelevant.