There’s a “Goldilocks Principle” as Dr. John Sorflaten describes at Human Factors International.
Goldilocks went into the three bears’ home and tested their chairs, beds and porridge, until she found what for her was “just right” (or so the fairytale goes).
His article Using the Goldilocks Principle to get design "just right" fits in very neatly with the theme of this “leave good enough alone” blog.
Go take a read of it, and find out how to apply the Goldilocks Principle to design.