You see the same thing over and over. Organized violence of any kind is one of the most chaotic of human endeavors. Unpredictability combined with high levels of stress produce huge amounts of unforeseen scenarios. Seemingly simples things go wrong in ridiculous weird ways.
The only way to mitigate that is through training, drill and preparation.
Hard commodity for the insurgents and terrorists, who usually operate under the constant threat of a raid, and who must prioritize secrecy over training. That's why when they do acquire base areas that are relatively safe from constant interference by the counter-insurgent/anti-terrorist forces, their efficacy increases exponentially. Absent that they are down to stabbing attacks, or an individual shooting spree.
Coordinated, multi-pronged attacks by several cells are very, very complicated operations.
9/11 required years of preparation by Al Qaeda in the Taliban-provided safe haven of Afghanistan.
Charlie Hebdo was hatched in the highlands of Yemen, controlled by the local affiliate of Bin Laden's shop of horrors.
Paris atrocity, almost certainly, was the work of jihadis who'd gotten their experience and training in Raqqa.