The hierarchy-of-effects model is a predominant advertising theory that shows how advertising works through a step-by-step process. It can be visualized as a pyramid, with awareness and knowledge of a brand at the bottom and actual purchase behavior at the top. The model proposes that advertising first builds awareness of a brand, then increases knowledge about what it stands for, then forms liking and preference toward the brand before ultimately convincing customers to purchase it. As consumers move up the pyramid through each successive step, the percentage who reach the next level declines.