Described in 1978 by Pauline Clance and Suzanne Imes, in women with high academic achievement. Later research showed it appears just as often in men and across nearly every field.
The core is an attribution loop: success is attributed to external, temporary causes — luck, timing, other people's leniency — and failure to internal, stable ones: “I'm not good enough”. That way every outcome confirms the belief. Positive evidence has nowhere to land.
Hence the two typical behaviours, opposite in form and identical in function: overwork (if I work three times as hard, perhaps it won't show) and delay (if I finish on the last night, a weak result is explained by time rather than by me). Both protect the belief, not the person.
It is not a diagnosis. It does not appear in DSM-5 and is not a disorder. It is a common cognitive pattern, and it is more frequent in settings where someone is the only one of their kind in the room — which makes it partly a problem of context, not only of individual psychology.