As an advertising tool, banners have been widely adopted by online marketers. However, because of low click-through rates, banners' effectiveness has been questioned. A phenomenon called "banner blindness" suggests that salient stimuli, such as banners, are often missed by Internet users. This contradicts the distinctiveness view which argues that salient stimuli are more likely to attract users' attention. However, the underlying mechanisms that cause "banner blindness" are still not well understood. Based on dual-processing theory, we develop a model to explain why and how banner blindness occurs. Specifically, we propose that banner blindness occurs because users actively or automatically control their attention to banners. Additionally, in controlled banner suppression situations, users' motivation- and capacity-related factors determine the degree of banner blindness. Conversely, when banner suppression becomes automatic, a user's habit of suppressing banners becomes an important factor affecting the degree of banner blindness. We propose that habit moderates the relationships between motivation, capacity, and banner blindness.