Planning

Imagine a pedestrian emerging into your path from behind a parked van. An inattentive driver will be taken by surprise, breaking suddenly, but perhaps too late to avoid catastrophe. Even if a collision with the pedestrian is avoided, the sudden breaking may cause a following vehicle to collide from behind. All this can be so easily avoided with a little planning and anticipation. 

Now imagine the same situation, but with the driver scanning the view from side to side and planning for various possible eventualities. First of all, this driver will have identified the parked van as a potential hazard, and will be actively looking to see if anyone or anything is likely to emerge from behind it. Is anyone moving into the area that is hidden from view behind the van? Are there any feet visible beneath it? Is there anyone visible inside the van, who may be about to open a door? Could the van be about to move off? If space is limited, this driver will already have reduced his speed on approach to the parked van. 

This is because he is planning for the possible eventuality of having to deal with one of these hazards. The possibility of dealing with such a hazard is the result of his anticipation of possible or likely events. Crucially, he is ready before he needs to be ready. He has already checked his mirrors and knows exactly what is behind and to the sides. His speed is already coming down, and his brake lights are visible to following traffic. He is actively searching for any developing hazards, and he is alert and poised to take any necessary action.

Once a specific hazard is identified, this driver doesn't only know about the hazard, he knows about everything that is going on around him. Because he has already reduced his speed, he has plenty of time in which to devise a suitable response. He can respond in the safest possible way, taking into account the time and space available, the specific hazard he has just identified, and the other road users in the vicinity.