It's not too hard for a person of average talent to earn a 10 handicap. It is twice as hard to get to a 5, twice as hard again to get to scratch, and twice as hard again to get to +5, which is about where one needs to be to even consider trying to qualify for the PGA Tour.
Talent, hard work, etc., all are inportant.
Yet there are lots of plus handicaps who have never even contended in their state amateurs and opens, and have no shot at playing professionally. Why?
They are students, or insurance men, or fathers, or whatever, and that is how they define themselves. Those that make playing golf a successful career define themselves as professional golfers. How many times have people on this forum decried the selfishness, egomaniacle attitudes of many tour players? Well, its no surprise, is it, that someone who excels playing this very difficult sport under very trying conditions using their own money to pay expenses with no guarentee of success are or become that way. And that some of them can't turn it off when they are away from their "office," unless that are with an insider- another player, a trusted media type, etc. Professional golf at that level demands self centeredness, at least on the course or at practice. And these days, the golfer as celebrity only magnifies the situation, what with all the attention focussed on them at all times.
Anyway, the answer in my book is: they define themselves and their lives that way.