I sometimes feel like I don’t know how to deliberately come up with ideas at all, but I’m not sure if I’m actually like that (it’s probably just insecurity or something, lol).
Do people like that actually exist, though? If so, why are they like that? And how do they learn to deliberately think of ideas?
Not sure to understand your point.
Ideas don’t come out of emptiness. They never. There is no such thing as some genius that get a brand new idea all by themselves out of their unique genius mind. Ideas are always the consequence of some kind of interaction with other pre-existing ideas and/or with other persons and situations. Direclty or indirectly (say, by reading a book). Genius may help, but it still requires something for the idea to grow out/on.
Talking about books, someone rightfully mentioned Descartes. Even him, who doubted absolutely everything, the whole universe around him and even he himself existed as an a person, in order to reach what he would consider a trustworthy certainty (cogito, ergo sum, I think therefore I am). Even that dude still needed the existence of a God to be certain that the fact that he was thinking (aka, that his idea of what he was doing) could be considered true or, at least, reliable enough to build upon. Ideas don’t come out of nowhere and never grow out of nothing.
Dislaimer: no René Descartes was harmed during the caricaturing his thoughts ;)