It's not just a coding exercise; it's also a game you can play sitting/standing in a circle with other people. I say "one", the person to the right of me says "two", but you know what happens at the special numbers. I initially thought you were asking why people mess THAT up and... it's actually pretty easy to mess that up, especially on sadistic mode where you're doing it as a circus warmup and doing squats with every count.