This is the best post here.
As NBEast mentioned, a lot of it is effort and time. If you think putting 40 hours a week in, 9-5 is going to suffice then you are horribly misled. You will be working most weekends, late nights, struggling through relationships, having to miss birthdays and weddings. Have great artistic abilities is important, but in my opinion Drive/Ambition is the largest part, followed closely by business skills. Actual artistic ability is just behind that.
There are a ton of crappy photographers out there who make a living photographing. They are great entrepreneurs, and work their butt off. I would love to be one, but I honestly am not willing to sacrifice what is necessary to get there.
I have a full time profession, a family, an hour commute each way. I loved taking a wedding or portrait gig 'cause I loved the interaction.
Eventually it got wearing to spend much of my free time away from my family or in front of a PC editing. It became a chore.
So I cut way way back. That led to diminishing skills. Found myself fumbling at critical moments if something unexpected happened. I finally decided its really just a hobby for me. I'll do some freebies but I'm done having the pressure of being "the pro".
I could see a clear path to success if extreme diligence, hard work, tolerance, marketing technique, etc were applied. Its probably a lot tougher to break into these days but, IMHO its a real possibility.