Ask HN: Concepts that clicked only years after you first encountered them?

Ask HN: Concepts that clicked only years after you first encountered them?
669 comments on Hacker News.
I'm reading Petzold's Code [1], and it dawned on me that I didn't understand logic gates intuitively until now. I took a Computer Architecture course back in college, and I understood what logic gates meant in boolean algebra but not empirically. Petzold clarified this for me by going from the empirical to the theoretical using a lightbulb, a battery, wires, and relays (which he introduces when he talks about the telegraph as a way to amplify a signal). Another concept is the relationship between current, voltage, and resistance. For example, I always failed to understand why longer wires mean more resistance while thicker wires mean less resistance. [1]: https://ift.tt/g5XW02w