I'm not sure I'd draw the line quite that starkly -- it's possible to build software or animate a film solo, but still get feedback from users or trial watchers

I'm not sure I'd draw the line quite that starkly -- it's possible to build software or animate a film solo, but still get feedback from users or trial watchers. I certainly believe that having a single mind -- or at most two or three people who understand one another super-well -- setting direction often leads to better results than strict "team" efforts.