Have you ever seen the movie "All About Steve"? Mary, the main character has these red boots that she ALWAYS wears. People make fun of her for it, but I think she is genius.
Or what about the movie "Confessions of a Shopaholic"? The main girl in that movie has a green scarf that she wears all the time.
One stable piece can dress up your outfit, or dress it down. It can be your best friend.
For me, my stable piece might be my gray converse, or new clogs I just bought. It could be a belt, pair of earrings, headband...They go with almost anything and can dress something up or down. It's a big money saver too when you think about it. That is one thing I am all about is to save money. If you have one piece that fufills your outfit's every need, that's great. I think one thing that people automatically think when they hear "stable piece" is black, white, or gray. I even think that. They are neutral colors, that "go" with anything, but I think that if your "stable piece" is a crazy color like red or seafoamy green, it can make your outfit even better. Whether you are trying to make your outfit look less like a hobo's...or you just feel like wearing that piece that day! A outfit is like a sentence(stay with me here). You need certain things everytime you make a sentence, like a period. Then you have other things that you throw in like subjects, verbs, nouns, etc. So what will be your period(stable piece), and what are going to be your other pieces(subjects, verbs, nouns..)? You make the choice.