It likely comes from the saying similar to this one: "kill a few, you are a murderer. Kill millions, you are a conqueror". More generally, we tend to view numb

It likely comes from the saying similar to this one: "kill a few, you are a murderer. Kill millions, you are a conqueror". More generally, we tend to view number of causalities in war as a large number, and not as the sum of every tragedies that it represent and that we perceive when fewer people die.