Multi tasking is a habit common among every human;mostly among the teenagers and young adults.While some people feel they can focus on various at a time it had been argued by psychologist that we can't do it as your attention is going to be divided without you paying total attention to what you are doing and that results in drastic reduction in performance.
It has been argued that those that multitask are people that can't focus on one action so they derive contentment by doing other things to take their minds off their immediate action for instance ,a driver making a call .While it is advisable for a student to doodle when sleepy during a lecture to regain his attention,it is not advisable for a person driving to make calls while on it as it will result in shift of attention resulting in a possible accident.