I don't think necessity is the mother of invention. Invention, in my opinion, arises directly from idleness, possibly also from laziness - to save oneself trouble.
That was what, ultimately, war did to you. It was not the physical dangers--the mines at sea, the bombs from the air, the crisp ping of a rifle bullet as you drove over a desert track. No, it was the spiritual danger of learning how much easier life was if you ceased to think.
He was very much a man of moods, possibly owing to what is styled the artistic temperment. I have never seen, myself, why the possession of artistic ability should be supposed to excuse a man from a decent exercise of self-control.