And when you do slip, and realize - with hindsight - that you should've done this or that, filmed this or that, focused on this or that... it's probably best to be mad at yourself for about an hour or so (really let that negative reinforcement sink into the core of your nervous system) ...
...but then, man, just let it go.
So many iconic documentaries have iconic documentarians who regret not being able to include X, Y, and Z because of the circumstances.
What appears to us as a classic work of cinema, to its creators feel incomplete.
But you don't know that, because you only see what you see.
The same goes for your own work.
Make what you have work, or go out and film more.
That thing you missed?
Hate yourself for about an hour, then let it go.
It's easy to realize what you should've done, in hindsight.