**Cannabis** affects driving mainly because it **alters the perception of the environment**. This means that, when consuming cannabis, you may see the environment differently, such as perceiving colors differently. This alteration in perception can make it difficult to clearly see traffic signs or traffic lights, which is crucial for safe driving.

Additionally, cannabis can cause you to lose concentration and require more time to react to situations on the road. These combined effects increase the risk of accidents, as you cannot correctly assess what is happening around you. Therefore, the **alteration of the perception of the environment** is a key factor that makes cannabis consumption dangerous when driving.