Cinema is (as I ignorantly understand it) a collaborative effort. In my amateur explorations of the craft, I've learned how important the editor can be. Taking reams of film, sometimes redundant, and choosing what to use, in what order, to best make a film flow.
Except when they don't.
Ever seen that film that's like "why in the **** is that happening?" that on later reflection/viewing you say, "ohhhh, editing!"
For me, The Dirty Dozen. WTF was Richard Jaeckel's Sgt. Bowen doing on the suicide run? I have to wonder if somebody cut a screen where he's there to punish him and/or make sure Lee Marvin's Riceman doesn't get fragged.