To me, the most impactful takeaway was from his interview about making Adaptation:

I remember sitting down one day and thinking, "What I'm I thinking? Where's my energy?" And my energy was on my complete blockage."

What a way to hone in on your key issue! - Where are you focusing your energy? In his case, his energy was on how to adapt the story - and that was the real story as it turned out.

I applied the same formula to two stories I'm working on and I suddenly see the heart in both projects - it's the surprise ending (duh!). I was trying to explain how the ending came about, but my energy was on the ending itself, how it was surprising, compared to what I expected. I was trying to make the stories more linear so the ending would make sense in the scheme of things. The result is I now see how I can improve the stories during rewrites by realizing that the endings are so out of the scheme of things that that is the true story.

It sounds confusing, but it is what really impacted me.