The left mouse button is typically the primary button on a computer mouse, used for selecting, clicking, and dragging items. Conversely, the right mouse button is usually the secondary button, often used for accessing context menus or performing specific functions depending on the application.

The distinction between the left and right mouse buttons is rooted in the ergonomic design of the mouse, which is intended to be used with the dominant hand of the user. In the United States, the majority of the population is right-handed, which is why the left button is designed to be pressed with the index finger and the right button with the middle finger. This design allows for a more natural and comfortable grip, reducing the risk of repetitive strain injuries.

According to a study by the Human Factors and Ergonomics Society, approximately 90% of the population is right-handed, which explains the prevalence of the left mouse button as the primary one. Additionally, a survey conducted by Logitech in 2019 found that 85% of respondents use the left mouse button more frequently than the right. These statistics highlight the widespread adoption of the left mouse button as the standard for computer interaction.

The left mouse button is also favored due to its role in the primary navigation and interaction functions of a computer. For instance, clicking the left button is the standard method for selecting text, icons, and other elements on the screen. The right button, on the other hand, is often reserved for secondary actions, such as accessing a context menu or performing a specific function within an application. This distinction in functionality reinforces the left button's status as the primary choice for most users.

In conclusion, the left mouse button is the primary button on a computer mouse, used for selecting and interacting with items on the screen. This preference is driven by the ergonomic design of the mouse, the right-handed majority in the United States, and the standard navigation functions associated with the left button.