My best friend is a wildlife documentary maker and we often discuss the differences between our fields. Another example is that in his field, everyone's idea is their big secret, while in the startup world, you're constantly reminded that your idea alone is worth very little and that you should talk about it as much as possible. I think the underlying difference is that when you're making a documentary, it's impractical to run "lean" or gather feedback from the market before it's done. You raise money once (based primarily on your idea), then you go to the ___location and shoot, then you do the montage, etc and ultimately there's a (hopefully big) release. There's barely any feedback loop to speak of.