The story of Goldilocks tells of a little girl who seeks food and shelter in the Bear family house. Going through the house she finds that the papa bear bed is too hard, the baby bear bed is too soft, but the mama bear bed is just right. That’s the Goldilocks principle: Having things just right. Not too much or too little but just right.
When designing user interfaces it can be tricky to understand what the user needs on a certain screenful. The solution is not to just show him everything, that confuses the user and makes him less likely to succeed. Here it is good to adhere to the Goldilocks principle.
SingStar is a game where people compete in who can keep a tune better. Every shower-singer can show off their talent for his (and others?) amusement. But as every shower-singer knows, what he is hammering on in the shower is usually just the chorus. In between choruses we quickly get lost. The lyrics + supporting music can help a little but usually this is not enough (just visit any karaoke bar). So how do you show the user what to do?
Visualising music has been solved centuries ago and professional musicians are very good at reading score and interpreting it (almost instantaneously) into music. However, reading score needs years of training so it is not appropriate for a casual game.
The designers of SingStar realized that the only thing the users need are the length of each tone and information on whether the tone is up or down from where they are. The players have often heard the songs before and their memory and feel for the song can guide them to the right tone (or there abouts) when they know roughly where they are going. No need for training, just start playing.
That’s an excellent example of the Goldilocks principle in action.