You are emerging from a minor road at a junction with the main highway. You see a car travelling towards you . You make a judgment; I could more than likely be out and up to speed before the car reaches the intersection.But you weigh possibilities quickly --and probably subconsciously--and stay put till the car passes.
Next day you leave the local pub with one whisky inside you. You arrive a moment or two later at the same intersection. You see a car coming toward you, at the same speed and distance as above. You confidently believe that you are ok to come out, and put the foot down, and come out.Probably perfectly safely. Probably. The point is , your CONFIDENCE was affected, albeit slightly, by that one whisky. And confidence affects judgment. The only safe level of alcohol is --zero.