Lots of good responses here, so I’ll give an example that blew my mind in a negative way: Fortran IV code, thousands of lines, no functions, only GOTOs jumping

Lots of good responses here, so I’ll give an example that blew my mind in a negative way: Fortran IV code, thousands of lines, no functions, only GOTOs jumping everywhere randomly. Mostly one or two letter variables, lots of GOTOs that turned out to be loops, with lots more jumping into the middle of them and jumping out of them into other loops. No documentation, I was supposed to modularize it. Failed. But it successfully calculated thermodynamic properties for engineering designs, so go figure.