Affordance

Why
Affordance as a design principle is important because it will allow the designer to design more intuitive systems for users

What
Affordance is the assumptions that people have about how to interact with certain objects or materials around them

Glass vs Wood
When vandals want to vandalize a bus station and it is composed of glass, they will choose to smash it. However, when the station is made of wood, they will instead carve and grafitti it. The material affords this kind of behavior.