I came up with my question after reading this one.
I've been in the face of a seemingly impossible problem a couple of times in my career, one of which I distinctly remember failing at (not my only failure by any means, just that this one stung). It was truly a bitter feeling, knowing that after months of work, I was only able to come up with a sub-par solution, and not having learned much in the process.
The above failure I mentioned was in a previous position, and it was a major reason behind my departure from my old company, because indeed, I didn't feel like a competent employee. Reading the question about resigning due to incompetence reminded me of those days. Thinking back, I can't help but wonder if I could have approached it differently...
So my question is: is it possible for us to objectively determine whether or not we are a good fit for the jobs/companies we are at? What questions should I be asking myself before I decide to "resign due to incompetence"?