Psychologists have written of how some individuals possess sufficient ambition to try but then, as they near their goal, begin to have doubts and engage in self-sabotage.
My guess is that behavior is fairly common. I've seen executives and managers whose careers are dotted with bursts of aggressively ambitious behavior followed by periods of significant insecurity. Lyndon Johnson once said Richard Nixon reminded him of a horse that nears the finish line only to suddenly turn around and run the wrong way.
These aren't people whose lack of ambition has taken them out of the game. If it had, their lives might be much simpler. Instead, they have the ability and drive to succeed and yet seriously question whether they deserve success. In many cases, less able competitors with little self-doubt wind up passing them.
The victims of this syndrome can usually be helped. The question is whether they will seek it.