Whether you call it the Sandwich Method, the Sandwich Rule, or the Sandwich Technique, keeping this simple style hack in mind will make your life easier when getting dressed. Think of the components of your outfit as a sandwich, with two pieces of bread on the outside and filling in the middle. One piece of bread will be in the top half of your outfit and the other piece will be in the bottom half of your outfit.
For example, in Look 1 below, the textured white/chartreuse striped blouse is one piece of bread and the white rattan platform sandals are the other piece of bread. The black pants in the middle are the filling of the sandwich. In the simplest terms, having white in the top and bottom halves of the outfit provides visual balance. However, also take note both the shoes and blouse have texture as well as a little bit of weight, i.e. the puffed sleeves and platform of the shoes, which further balances the look.
In Look 2 below you can see the white top and white pointy-toe flats form the bread of the sandwich and the light peach shorts are the filling. Both the white top and shoes have texture which add interest to the outfit and are of complimentary weights.
Although both examples discussed have shoes/tops the same color, it's important to know that's not necessary when utilizing the sandwich method. Equally important as the color of the shoe is whether it feels proportional to the rest of the look. For example, a white boot wouldn't have worked with Look 2 because it would be too heavy for the white cotton vintage embroidered blouse.
There are endless ways to apply the sandwich rule! The next time you feel something in your outfit feels a little off, try thinking of it in these terms and making adjustments accordingly.