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

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://www.codehiddenlanguage.com/