What is circle of influence?
Everything which we come across and we are in a position to alter is in our circle of influence. Everything for which we feel we are concerned that is in our circle of concern. It is ourselves who decide boundaries for our circles. What is deciding criteria for this? Is there any need to think for this? If yes then why?
Suppose you got the news that somebody in some other country killed his wife. You cannot do anything in this regard, so do you need to feel concerned about it, do you need to feel sorry for the killed one? There are many unpleasant incidences that we feel worried for, those incidences effect us which we cannot control in any way. If a normal person keep on thinking about such incidences then he can never be happy. But in case you don't feel for them, you feel yourself heartless.
Now coming to practical point of view. The incidences for which we cannot do anything, why should we think or worried about them? If they are not in our circle of influence why should we hurt ourselves? Moreover thinking and getting tensed about those things which are out of our circle of influence wastes our precious energy which could be efficiently used in giving our best in circle of influence.
If somebody died because of unavailability of blood, you are not responsible for it, but if you could give him blood but you didn't only then you are responsible. So the best way to live happily and satisfactorily is to make the boundaries for circle of influence and circle of concern exactly equal. It never matters what you think but what matters is what you do.