When Production Forces a Structural Rethink: Real-World vs. Ideal?

Hey everyone, Ngozi here. I'm deep into pre-production on a new feature, a gritty drama, and I've meticulously laid out a 4-Act structure. On paper, it's tight, every beat lands, the build and payoff feel perfect. But I'm also keenly aware that film production is a beast, and even the best-laid plans can get shredded. I'm talking about things like losing a key location, an actor's availability shifting, or even discovering in the edit that a sequence that felt essential on the page just isn't working on screen.

My question for those with more mileage: Have you ever started with a seemingly bulletproof structural plan (be it 3-Act, 4-Act, whatever) only to have the realities of shooting or post-production demand a fundamental re-think? What was your biggest 'real-world vs. ideal' moment concerning structure, and how did you navigate it?