How can mental alertness to prevent injuries?

From what I understand mental alertness helps you decide from what's dumb and what you should be doing like for example if someone went to go walk across the street it's your mental alertness that helps you see if it's safe or not... your mental alertness can transfer signals to your body why helps you stop doing it physically so if a car was coming and you were in the middle of the walking your brain censors the danger that is approaching to have you run across or to not cross at all; where as the driver mental alertness sees the danger on what's happening so that's put into physical alertness to stop the car but truly i dont know it's worth a shot