I could start an entire new thread about "Doesn't matter how long you've done this, dont get cocky, you've messed <this> up again."
My personal favorite is after 25+ years of using PVC for tank plumbing, I finally overtightened a threaded 1/2" elbow on a new external skimmer I'd added. And two days later, after I'd crashed in the hotel from long interantional flights for a business trip... I get the Double Phone Call. (calling twice in a row means, "Answer No Matter What's Happening.") Of course, alarms going off, dry bump screaming sounds in the background, and fish equipment room sprayed wet like a fountain had fired up in it. - because it had.
And... My wife wasn't home either, it was a neighbor who had agreed to just stop by and Feed The Fish.
In my sleep, I figured out how to diagnose. Talked them through unplugging the right pump cord. And manually refilling the sump from the Fresh-Saltwater vat, not the no-salt RO Evap makeup water vat. I was paranoid they'd add all freshwater and crash the salinity.
All worked out OKay. NO skimmer for a week was no problem. ... How many times have they told us its possible to use too much teflon tape in a threaded PVC joint, and if you overtighten the fitting can just crack?! There's always another valuable lession, just waiting to be taught to us.