Not easy to describe this. But it was important. Important to making it work, to making it succeed. I decided the setting, the football league, 4 divisions, plus a knockout cup, the FA Cup. I decided on what attributes your players would have. I decided what you could control. Then I pieced together the game balance. The balance between randomness and control, between complexity and ease of use. Various moving(mathematically) components interacting, finding the way to make it fun and easy but give the game plenty or range, so it did not repeat, was never predictable. And then it had to fit within the programming environment I had, and the small amount of memory.
It took a year to make.