For me, I can remember:
- objects are closures and closures are objects - properly getting the JS asynchrony model - pointers and the whole memory addressing model - HTTP being stateless
I must have had an early epiphany with function return values, since I remember not writing functions correctly at first, but I don’t remember the actual epiphany.
I think realizing that execution in imperative languages was one after the other and that there's a sort of "cursor" that goes through the code (execution flow/instruction pointer/whatever) was one of the first things that made things click.
I miss them, as they were incredibly endorphin-releasing moments.
But I must admit, the day I saw a guy run, essentially, "cpio ... | rsh otherhost cat > /dev/tape", that was a very "aha" moment in terms of overall system design and what networking brought to the table.