On that last note about assuming it works the way you think it works?
A personal anecdote, if you will? Early on in my cycle of rules writing for my (tabletop) starship game, I gave the rules to someone to have a go with and they came back next week talking about how is was quite hard to make a ship, because of the cyclic iteration of how the size changed everytime you added a system, because the you had to recalculate all the engine propotions and such, to my utter bafflement.
I quickly reaised that the ship generation was missing the kind of blindingly obviously line that the first thing you did was choose the hull size! It was such (to me and the others who'd played previous spiritiual ancestor games like Full Thrust) an obvious thing to do that it had just not occurred to me that line was missing. It can be rather easy to do! Idiot-proofing check indeed. Sicne them I have gotten very much more careful about making sure what I think I've written is what I have actually written.
So, I have some sympathy, at least, when stuff slides through.
Yeah, I know I've had my editors bring up one or two writing goofs where a character's actions/motivation made no sense, and I was baffled because it all made perfect sense when you considered the background and worldbuilding that was in my head ... but hadn't actually made it onto the page.