For a **seat belt** to be effective, it is essential that it is properly adjusted to the body. This means that the **straps** of the belt must be correctly positioned:

- The **chest strap** should pass over the collarbone, between the shoulder and the neck, and go down the center of the chest. If placed incorrectly, such as over the neck or a breast, it can cause serious injuries in the event of an accident.

- The **lap strap** should be over the hip bones, always below the stomach. If placed above, it can cause serious internal injuries in the event of an accident.

A poorly adjusted belt can reduce its effectiveness and increase the risk of injury. For example, the **submarining effect** occurs when the body slides under the belt during an accident, which is more likely if the belt is not properly adjusted.

In summary, a well-adjusted seat belt is crucial to protect vehicle occupants, preventing them from moving from their seats or being ejected in the event of an accident. Wearing it correctly significantly increases the chances of surviving an accident.