Everything you wrote is true.
I have a simple explanation that describes where confidence comes from.
Confidence is a feeling that comes from the thoughts that we have.
Our thoughts come from our experiences and our imaginations.
If we focus on reality, then we must consider our experiences.
If we have done things in our lives, and if those things we did turned out successfully, then we should believe that we could be successful again in the future.
If we have succeeded in the past, then we should believe that we could be successful again in the future, so we should think and feel that way.
That means we should be confident.
By the way, your discussion is well-written, so you should be a little confident about your English writing skills.
Where does confidence come from?
I consider myself confident in somethings, and not so confident in others. At work I am confident because I have been doing it a long time. In driving heavy machinery, trucks, cars I am confident. In my language I am confident. In relationships I am not confident, perhaps because I was confident in my marriage and it ended abruptly. In that moment my life changed profoundly, painfully. I am confident of my inevitable conclusion and this fact has made me realise something monumental which is this, nothing matters. Being rich, being poor, being ignorant, being educated, being famous, being nobody, we all die in the end. To me what matters is the time I have, I enjoy Monty Python, laughing at comedy, experiencing my life as I choose to live it.
Unable and confident => Overconfident : it's definitely not a good thing.
However, with the same level of ability, a confident person will perform better at doing a task or at learning something new (like how to swim or to speak a language) and thus will achieve more ability afterwards.
In some cases, the "Fake it till you make it" does work, though not always.