Look at this video, which i took at a place near my city-Bangalore, India. Monkey is trying to eat rice but it is turning all around with the fear that some other monkey will come and share it or some person will come and chase it out from there. Because of the fear, it was unable to eat it happily.
Same thing will happen to us when we are distracted by many factors when we are working. We cannot concentrate on our work. Quality of work will be reduced. If the distraction is too much, we cannot even complete the work.
So, when a work is assigned to a person, he should be allowed to complete the work. There is no point in forcing him to do something else.