Heh, it's always those things about ourselves that are extremely obvious to anyone who's met us that are hardest to see about ourselves.
My day job is military intelligence analysis, and I can tell you that 70% of the guys I trained with weren't capable of doing it in more than a rote or basic capacity. A third of those couldn't analyze their way out of their own museum, if you take my meaning. Fortunately, after their initial contract, none of those people who were unsuited continued to do it, they all found some other career specialty.
Art school can be similar, although it's a pricey way of doing it. When I went to college for an art degree (before the military), the main thing I learned was that I lacked both the technical and social skills to hack it as an artist professionally. It took me the full 4 years to come to terms with it, despite it being immediately obvious in our first critique that the students who had a parent or relative in the industry already were way more skilled and capable. There were other students in my boat as well, though I don't know whether they saw the writing on the wall the way I did (a couple of them I know did not!). I worked my tail off to try to catch up, but I honestly didn't succeed.
If I'd had the technical and social skills I have now (10+ years later), perhaps I could have been successful at it. Ah, well.
All that is to say that eventually we figure it out and find some other career (I'm great at my day job, wish I'd known it was a career field when I was in HS/college) more suitable, or else keep failing at it for ages like Tom Preston. The first category will hear your critique, the second won't listen. Either way, it is painful.
It has been remarkably difficult to get good critiques online. I know my work isn't yet where I want it to be, and I'm past the point where well-known solutions and basic analysis can get me on my own.