One of my professors in college put it in a way that stuck with me. All source code has to be compiled by (at least) two different machines; the compiler and t

One of my professors in college put it in a way that stuck with me. All source code has to be compiled by (at least) two different machines; the compiler and the programmer's brain. The machines have radically different parsers, but must end up with the same parse tree for the program to function correctly.