What really made computers click to me was reading a book that had the premise: "learn just enough assembly to be able to implement C features by hand; we'll show you how". Sadly, I don't remember the title.

Another revelation much later on, was, as discussed here, the realisation that C is indeed defined over an abstract machine. I think much of those realisations were because of reading about how crazy compiler optimizations can be and how UB can _actually_ do anything.