The terrorist attack in Paris, as recorded by the witnesses, the same people that run away on the building roofs, was hard to take. The repetition of the few informations, the streaming of the images of the shooting at the policeman was too much.
The first thing I though was the Madrid bombing in 2004. At that time, 11 March 2004, facebook was just one month old, and posting and sharing was far for being an indicator of public opinion. Yet, almost 200 died that day while going to their routine duties. That was hard to take and to forget, although it seems that indeed it has been forgotten.
But if you search (the easiest way, wikipedia) you learn that on the first 7 days of the year, the one in Paris was the 14th terrorist attack. The list over the years is escalating, unbearable. However, if the school shooting of last December (less than a month ago) is old news, you may understand that 2004 is archeology.
Moreover, if you search for wars (again the easiest way) you realise that there whole planet is at war, conventional or civil or terrorist war. Just pick a Nation.
How much we will remember? How much can we take? How much before we realise that there is only one world? in short, how much is too much?