a) people who lack the insight to realize it, and thus don't work to fix it b) people who realize it but don't care (for various reasons, some valid some not)
If you're agonizing over your job competence and trying to improve but feel you aren't succeeding, then it's vastly more likely that either your job specification is impossible, or you're setting unreasonable personal goals around your job.
There's also a chicken and the egg issue here; perhaps the author really does not enjoy coding and thus is not willing to put in the effort to improve?
None of that is in question, but let me ask you this: are you a professional basketballer?
I'm not a professional chef, read into that as you will.
It's very possible to be bad at something AND know that you're bad at it AND not be able to reach the proficiency to perform the task at a professional level.
Also, it's pretty clear that I can read. If you are going to insult me, it's better to insult my comprehension or argumentation. However, I would argue that it's generally better to just not insult other people.
You forgot to add "AND still be employed in that capacity."
When I doubt my dancing skills, it's a rational evaluation.