One of the biggest driving forces in programming is understanding how stuff works. Apart from the satisfaction of understanding, it also gives me confidence in the code I write myself.
The software I work on is usually dependant on numerous external software packages, with which I only interact through documented APIs.
I would love to understand how it works under the hood, but every time I venture into unknown codebases, I feel immediatelly lost. For every answer I find, I have 5 more questions, growing exponentially. I feel overwhelmed, discouraged, and dumb.
I know this line of thinking is wrong. Writing software is a hard discipline, requiring a lot of time and effort -- of course it takes just as much understanding it!
I know from other disciplines in life that having this "I can't do it" mentality will doom you from the beginning. Keeping an open mind and having patience is key. Knowing this rationally is not enough, you have to convince yourself and actually believe it.