Stairs are divided into left and right primarily for safety and convenience. This design ensures that individuals using the stairs can navigate them with ease and reduces the risk of accidents. According to the National Floor Safety Institute, falls on stairs are one of the leading causes of injuries in the United States, with an estimated 12,000 stair-related injuries occurring annually. The left-right division of stairs helps to maintain a consistent pattern that users can anticipate, making it easier to balance and avoid missteps.

The concept of dividing stairs into left and right is rooted in the natural human tendency to favor the right side of the body. This preference, known as lateral dominance, is observed in various aspects of human behavior, including handedness and spatial navigation. Studies have shown that the right hemisphere of the brain, which controls the left side of the body, is often more dominant in processing spatial information. As a result, individuals are more likely to navigate stairs by favoring the right side, which aligns with the traditional left-right division of staircases.

Additionally, the left-right division of stairs is influenced by historical and cultural factors. In many cultures, including Western societies, there is a long-standing tradition of placing the main entrance to a building on the right side. This practice, known as the "right-hand rule," extends to the design of staircases, ensuring that individuals entering a building can easily locate the stairs and navigate them without confusion.

Data from the Centers for Disease Control and Prevention (CDC) further supports the importance of the left-right division of stairs. The CDC reports that falls on stairs account for a significant portion of emergency department visits and hospitalizations related to falls. By dividing stairs into left and right, designers and architects can help mitigate these risks and create safer environments for individuals of all ages and abilities.

In conclusion, the division of stairs into left and right is a crucial aspect of staircase design that enhances safety and convenience. This practice is influenced by human biology, cultural traditions, and the need to minimize the risk of accidents. By adhering to the left-right division, designers can create staircases that are intuitive to navigate and contribute to a safer built environment.