What’s the Most Absurd Game Mechanic That Would Fail in Real-Life Civil Engineering?

I was playing a game recently where you could just slap materials together and they’d magically stay in place, no matter how unstable. Got me thinkingwhat’s the most ridiculous game mechanic you’ve seen that would absolutely never work in real-life civil engineering? Like, instant bridges or buildings that defy gravity? Curious to hear your thoughts!