Why don't aircrafts collide in the air?

The risk of aircraft colliding is taken care of by flight controllers, They see to it that all aircraft take off, fly, and land in the areas assigned to them. If an aircraft accidentally flies beyond its area, the flight controller usually hands over the control to a colleague. All flight controllers carry out their work with the help of the flight radio-a wireless network for communicating with the pilots-and the radar, with whose help they can located aircraft on a special screen. In this way, every aircraft is controlled and monitored over the entire stretch of its journey. Flight controllers work in a control tower, from where they observe and control the take-offs and landings.