Most of us don't understand many complicated things we interact with in a regular basis. Back to even the simple cases of what happens when I type something in this form, and hit enter. Every keystroke is a bunch of work, by a bunch of devices talking to each other through complicated protocols, just to get to memory, which will get to my screen, eventually... and that's pretending we don't care about how physics works, because it's reliable. It's all overwhelming.
And if we only focus on the unreliability, look at many bugs in our systems today. Why does this crash with some input? Why does a new enough processor have security vulnerabilities, so someone can steal passwords? All might as well be magic, even though a few humans, somewhere, might know the reasoning.
And if AI feels difficult, imagine biotech. I could, theoretically, mess with weights and retry a prompt over and over again, seeing what changes. It's a lot of work, but it can be done. See how much fun we have figuring out what a single nucleotide polymorphism does phenotypically, and why it does it: It's a research project by an expert in the easiest of cases! We are only a little ahead of the new C programmer changing things at random to see where his pointer math went wrong.
We don't understand how anything works. We are just sometimes satisfied with our degree of ignorance, and decide to stop asking questions.