Behold, the duality of engineering! At the top, we have the "Regular Engineers" (portrayed by Potter and Weasley) screaming in terror when something goes wrong. Below, the "'It Only Needs To Work Once' Engineers" represented by a sinister Tom with that devilish grin that says "consequences are someone else's problem."
After 40 years in the field, I've seen both types. The meticulous ones who triple-check everything, and the chaos agents who build rockets with duct tape and optimism. The latter are usually found in startups or final-year projects approximately 12 hours before the deadline.
Remember the Mars Climate Orbiter that crashed because someone mixed up metric and imperial units? That's what happens when you let the "it only needs to work once" crowd near space hardware.