That "blown core" situation is NO JOKE. It seems like a small step, but mold wash stops the metal from fusing to the sand. When that happens, you're looking at HOURS of extra work to chip out the casting. The cost of re-melting everything totally wipes out any time you saved. I learned the hard way too, now I treat it like the MOST important part of the setup. It's one of those things that feels pointless until it saves your entire batch.
Had a similar wake-up call with woodworking finish. Skipped the sanding sealant once to save time, and the stain blotched so bad it looked like a toddler painted it. Now I never skip the prep steps, no matter how tedious they seem.
My guitar tech always says a quarter-turn of the truss rod is the difference between a playable instrument and firewood. It's the same idea, a tiny adjustment that feels like nothing until you skip it. I've seen a neck warp over one humid summer because someone didn't do that basic seasonal check. The repair bill was more than the guitar was worth. What other fields have those invisible make-or-break steps like mold wash?
Honestly, it's wild how many fields run on these tiny, thankless tasks. It makes me wonder, how do you even train someone to respect a step that seems so trivial? Is it just about making them live through the disaster once, or is there a better way to pass that lesson on?