IF THE SHOE FITS .....

 ... wear it!

What size do you think this shoe is?  It definitely does not belong to Cinderella :>)

Here are a few expressions associate with "shoe" -
I wouldn't want to be in your shoes;
The shoe is on the other foot;
(I am not sure what this expression is about) The shoemaker's kids always go barefoot!
Hey QQ, how about, "Have shoe will run"?