If you started with iOS development, it's not very hard to believe that you struggle to pick up fundamental paradigms of computing. Apple has long been about abstracting things away from the user, and over time that philosophy has started to spill over into the way they treat development too. Some people love it because it makes it so they don't need to learn the boring stuff, and other people despise it because you never get to solve truly interesting problems and are ultimately at the behest of a multi-trillion-dollar corporation. One thing is certain though: you aren't getting the full picture.
SICP is about expanding your mind as a developer, which is a painful process that most people don't notice as they learn to program over extended periods of time. Not understanding it doesn't make you dumb, it's just particularly heady stuff that's intended to stick in your brain. There's a reason why people treat SICP like a bible; it's an allegorical exploration of computer science, not necessarily rooted in raw truth, but more intended to help you realize the awesome scale of the modern computer and the people who program it. Being humbled by that book is just part of the process.