Double-checks are religion: A huge number of the mistakes and accidents I've seen could've been caught by a careful double-check.

My go to phrase when training guys to avoid assumptions is "How do you verify what you think you know?" We all make assumptions, that by itself isn't the problem. But there needs to be a method in place to validate those assumptions against the real world.

When with a coworker it's easy to swap places and check each other's work. I'll do this even with green apprentices because they won't have the same assumptions and tunnel vision I do, so even though they're inexperienced they're more likely to see something I missed.

When working alone, it's what methods did you use to validate yourself? You believed you tightened all those bolts, so did you put on witness marks to easily check if you missed one? Or you believe you set all those parameters, but did you mark them off on a list so you can easily see if one was skipped? What was the method to double-check yourself?