I would fail if I had to work with stars. And I also can't afford to work that way. I can't afford to have special circumstances for rarified individuals. So, I work with actors who have given me a sign that they're willing to work in these more humble circumstances, in real-life locations.
You have so much more time to observe and learn with a documentary because of the time between the shoots. You get a much deeper understanding of day-to-day life and its themes. It's also much more of a mess after three years; you have to comb it out carefully and see what fits together and makes sense.