What is the support to the brand promise? The Reason Why, aka Support to the Brand Promise, is part of the Copy Strategy and it helps customers believe the promise (benefit) the brand makes, so it is linked to the brand benefit, if any. It is not always used. When used, however, it must link to the benefit and possibly to the product too; and 

it should be tangible, realistic, comprehensible and visible.

The brand Support is often found in:

• Product formulation – f.i. kind, quantity, quality, absence or presence of certain ingredients (Swiffer and most P&G brands)
• Product design – physical elements (Duck WC)
• How the product works (Gillette razors)
• How it is produced (Pasta Voiello)

Brands without benefit and without support can still differentiate through the Brand Character.