First-time Filmmaker: Most Catastrophic Pre-Production Mistake?

Hey everyone, I'm a writer/director and I'm gearing up for my first independent feature. I've done a lot of research, and there's no shortage of warnings about pre-production pitfalls, everything from incomplete scene breakdowns to a complete lack of sound design planning. It's a bit overwhelming to be honest.

I'm trying to be meticulous, building out my shot lists and trying to anticipate every need. But I also know that as a first-timer, I'm bound to miss something crucial. I've been focusing heavily on my script breakdown and trying to secure locations.

From your experience, which one of these common pre-production mistakes do you believe is the single most catastrophic for a first-time indie filmmaker, the one that can truly derail a project entirely?