The instability and malleability of personality
When I was educated as a psychologist, in the 1980's, the dominant way of thinking in psychology tended to what we would now call a fixed mindset . Roughly, as students, we were taught that both intelligence and personality are hardly malleable from a certain age on (say, 18). Personality was roughly defined as the whole of stable behavioral tendencies of individuals. It was thought that individual differences in personality were relatively stable and also meaningful, for example for how we should make career choices.