It's not that far-fetched. A few years ago, Peter McGuffin, a psychiatrist and geneticist at the Institute of Psychiatry in London, was working on a study of depression when he stumbled on something interesting. He checked identical twins who lived apart. He concluded it had something to do with inherited personality traits. Depressed and pessimistic people report more bad luck.
Optimistic people report less.
In effect, he is saying what Carville is saying. That some people just keep popping back up. They are not defeated by failures. They are indefatigable optimists, and they put themselves in a position to field good luck when it arrives. In Clinton's case, his humble beginnings are often cited as examples of bad luck.