Things that blew your mind as a programmer and/or computer scientist?

Question

Things can include anything. It may be a new programming language, a book, a course, a new tool or utility, new theory or algorithm. Just anything that blew your mind in a positive transformative way.

noob_eng · Accepted Answer

Structure and Interpretation of Computer Programs. That ONE book was enough to get me programming more and more.And also building tiny projects on my own interest.

AnIdiotOnTheNet · Answer

Tricks of the Game Programming Gurus by Andre LaMothe[0] blew my mind as a young kid who liked video and computer games. It took all this amazing stuff I was seeing and from more-or-less first principles[1] showed me how it all came together from applying a little logic and math.
I still have a copy to this day, missing both front and rear cover and with with significant wear throughout. Unfortunately I don't appear to have the disc that came with it[2].
[0] https://archive.org/details/tricksofgameprog0000unse
[1] Chapter 2 is called "Assembly Language Basics".
[2] https://archive.org/details/Tricks_of_the_Game_Programming_G...

wsgeorge · Answer

Abstractions as a concept. Can't unsee them now, 14 years on.