The stupidest thing I have ever done...

About 20 years ago, a guy who was friends with my neighbor spent a ton of money building a nice Ford big block. Forged rotating assembly, high dollar rods and pistons, trick aluminum heads, the works. They assembled the engine in my neighbors garage, and were absolutely fanatical about keeping the shop clean, no dust, everything left in boxes or bags until the last minute... etc. They paid an unbelievable amount of attention to keeping things clean and building that motor as perfectly as they knew how. Every last detail was triple checked, re-measured and checked again. Nothing wrong with any of that, but I used to kid them about how long it was taking. Final assembly of the engine probably took 80 hours. The finished engine was finally installed in a cherry 1970 Torino. I guess the anticipation and excitement finally got the better of them... the night they were going to start it for the first time, they called me over to watch the fire-up. They had primed the oiling system, and even primed the fuel pump. Ignition timing was estimated to be as close to perfect at they could get it without running the motor.
My neighbor carefully poured a little premium fuel into the carb, and the proud owner jumped in and turned the key. The engine fired almost instantly, and immediately went to wide open throttle. Both guys were so shocked, they stood there sorta frozen, just staring at the thing going full throttle. It probably took me 15 seconds to run across the room and rip out a handful of spark plug wires from the distributor to get it stopped. In all their meticulous preparations, no one had thought to install a return spring on the throttle linkage. So much for a brand new high dollar motor.