Most Damaging Production Mistake: Post-Production Nightmare Fuel?

Hey everyone,

I'm Elena, a producer currently knee-deep in pre-production for a new series, mostly shot on my V-RAPTOR XL and an AMIRA, relying heavily on lavs like the COS-11Ds into a Sound Devices 833. I've been poring over various production best practices, especially around on-set audio and lighting protocols. There's a ton of great advice out there, highlighting issues from clothing rustle, generator hum, to not white-balancing properly with our SkyPanel S60-Cs.

My brain is spinning trying to prioritize all these potential pitfalls. From your collective experience, what's the single most difficult common mistake to truly fix in post-production, one that inevitably snowballs into larger creative or budgetary problems down the line? I'm talking about the kind of issue that makes editors weep and colorists pull their hair out, even with the best tools.

What's the absolute worst thing to miss or mess up on set?