[dgordon]

"Think about this: you IQ is defined and practically unchangeable by the time you are a young teenager, but your personality continues to develop for many more years after that. So there is no way your personality can affect whether you are smart or not."

I don't know whether the two claims you made are true (the one about IQ may be, the personality one probably is) but "there is no way your personality can affect whether you are smart or not" doesn't follow. It's possible that your personality may often continue to develop after your IQ is mostly set, but only in a highly restricted way dictated by what your personality was before. In fact this seems to me likely to be a common outcome.