Programming and mathematics. Mathematics is the foundation of programming.  A computer is basically just a large mind with a long tape, which records.  When you feed information to the computer, it records it in an organized and "understandable" form, or a process of "thought".  Every once in a while, a computer can take in a memory and create something that's harder to understand.  The most common example is a computer that recognizes images and reads their file. 
Math is also hard because it's limited to thinking of formulas, equations, and using logic.  It's easy to throw around words like "logic" or "equation", but if you could think in a language like English, you would be able to prolong the understanding of similar concepts and do what Bach did - just play the fuga.